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The objective of this study was to determine which personal, environmental and occupational factors were associated with risk of non-fatal ischaemic heart disease in a group of 3930 white underground miners born between 1916 and 1930. Evidence of previous myocardial infarction, based on their electrocardiograms and answers to the Rose questionnaire, was found in 179 men who were taken as the cases of interest. Because of difficulties in coding the occupational histories of all available miners, a representative sample of the remaining 'non-infarct' miners was drawn as a reference sample. Univariate analysis of the 179 cases and 669 referents showed that the personal factors such as age, systolic and diastolic blood pressure, serum cholesterol and smoking were significantly different in the two groups at the 1% level of significance. Logistic regression analysis showed similarly that these same variables were significantly associated with IHD when included in a multivariate model. None of the environmental and occupational variables was significant.

A cohort of 3971 white miners in South Africa, born between 1 January 1916 and 31 December 1930 who were alive on 1 January 1970 and currently working in the East Rand-Central Rand-West Rand mining areas, was followed up for nine years, when the 3426 survivors were aged from 48 to 62. Fifteen (0.4%) had been lost to view and 530 had died (13.4% of the 3956 whose vital status was determined). Based on the occupational histories of a 30% sample of the cohort it was known that the vast majority were gold miners. An estimated 93% had worked more than 85% of their mining service in gold mines. Standardised mortality ratios were calculated as the ratios of the deaths observed in the cohort to those expected on the basis of concurrent mortality in the reference population--the total white male population in the Republic of South Africa. There was little sign of a "healthy worker effect"; of several possible reasons, one is that the white miner in South Africa had adopted certain unhealthy life styles, another is that the reference population was otherwise inappropriate. The SMR for all causes of death (117.6) was raised because of excess mortality due to the following causes: lung cancer (161.2), chronic respiratory diseases (165.6), and acute and chronic nephritis (381.0). A case-referent analysis was carried out on those miners in the cohort who had spent at least 85% of their service in gold mines. For lung cancer, smoking was the main contributory factor towards disease. For chronic respiratory diseases bronchitis, emphysema, asthma, pneumoconiosis, and pulmonary heart disease), smoking was also the main risk factor, but there was an association wih cumulative dust exposure. Raised blood pressure, smoking, and adiposity were associated with ischaemic heart disease as was the duration of service underground. Study of comprehensive medical histories in all 530 deaths, including necropsy in most cases, showed that none was directly due to pneumoconiosis or to tuberculosis.

Four trained young men, worked for 4 h/day at 43–50% of their maximum aerobic capacity for 3 days at 25 degrees C db, 18 degrees C wb and then for 10 consecutive days at 45 degrees C db, 32 degrees C wb. Their thermal status was assessed using direct calorimetry. As a group, the men showed classical acclimization responses, but there were marked individual differences. The calorimetric analysis revealed that reductions in strain were associated with minor changes in heat balance confined to the first and last hours of exposure. Events occurring within the first 4 days appeared to have little effect on body temperatures. Significant decreases in body temperature took place only when sweat and evaporation rate increased. A 10% increase in evaporation rate was accompanied by a 30% increase in sweat rate and a 200% increase in unevaporated sweat; thus, there is a wasteful overproduction of sweat. By the 10th day skin temperature was confined to the level necessary to evaporate sufficient sweat to achieve thermal balance with a fully wet body surface. The efficiency of heat transport within the body did not change with acclimatization.

Various procedures are available for measuring an individual's maximum oxygen capacity. Most of them, however, are time-consuming, require expensive equipment and demand maximum effort from the individuals being tested. Investigations have been made, therefore, for the purpose of finding relatively less expensive procedures which would require sub-maximum effort only. Such procedures would have a wide use in the Human Adaptability Programme of the I.B.P., when the endurance capacities of different populations in various parts of the world will be compared. It will be essential, however, for these procedures to be standardised if valid comparisons are to be made.

Metabolic and thermal responses of three dogs were made in a rapid responding calorimeter at temperatures ranging from 8°C to 36°C. These dogs were acclimatized to a kennel temperature of 27°C and had critical temperatures between 23°C and 25°C. The only physiological responses to low environmental temperatures were a moderate decrease in total heat content and an increase in heat production. The tissue conductance and the cooling constant of the fur did not effectively decrease below the levels obtaining throughout the neutral zone. In a hot environment heat loss from the respiratory tract was greatly increased. Although there was a great increase in the tissue conductance in the hot environment, conductance of heat through the tissue became decreasingly important as the air temperature approached body temperature so that panting became increasingly important for maintaining thermal balance. It is concluded that the vasomotor response of the peripheral vascular system is primarily a mechanism for dissipating excess heat produced during exercise; it is practically unimportant as a heat conserving mechanism. Effective changes in the total insulation of the fur can only be achieved by changing the surface area of the body, particularly those areas which are thinly furred, and not by any important change in the fur thickness through pilomotor activity.

Two separate studies of the reactions to cold of one sample of 8 and one sample of 15 Kalahari Bushmen were made in their natural habitat and the results compared with the Bantu and, to a smaller extent, with the Caucasians. With a decrease in temperature from 27 to 5 C the metabolisms of all three groups rose. Metabolic rates per square meter of Bantu and Bushmen were similar, although higher than those of the Caucasians, but the percentage increases were closely similar for all groups. Rectal temperatures of Bushmen and Bantu were similar and decreased as the temperature dropped, while that of the Caucasians rose. Toe and finger temperatures of the Bushmen were higher over the whole temperature range than those of the Bantu and Caucasians, while the average skin temperatures were closely similar. Metabolic rates and rectal temperatures, therefore, indicate that subcutaneous tissue insulation against heat flow is greater for the Caucasians than for the Bantu or the Bushmen. Measurements of average skinfold thicknesses confirm this finding. Bushmen and Bantu reactions are quantitatively similar, but are qualitatively slightly different. From these findings we conclude that the difference between Bushmen, Bantu, and Caucasians is essentially morphological. desert and "river" Bushmen in the heat; effect of morphology on reaction to heat; heat reactions of Bantu and Bushmen; state of acclimatization to heat of Bushmen and Bantu; sweat rates of Bantu and Bushmen in standard heat conditions Submitted on October 21, 1963

A study was carried out to determine whether physical working capacity and mechanical efficiency at the task are important determinants of the level at which an individual performs a moderately heavy physical task under normal working conditions underground. The method allowed a number of important preliminary points about the underground task to be established. These were (a) There were significant differences between men's performances at the task. (b) In general, men maintained their rank order of performance at the task over a period of 5 months. (c) Local variations in the physical features of the underground work situation had a negligible effect upon the differences in men's performances at the task. The results of the study showed that neither of the two physiological factors examined was of any importance in determining a man's level of performance at the task, with the proviso that all men performing the task should have sufficiently high physical working capacities to enable them to pe...

The performances of two gangs of Natives were examined to determine the influence of the quality of European supervision on the mean performance of a gang. One gang, working under a European supervisor, produced close to their maximum with a fairly close scatter of individual performances about the mean for the gang. The other, under a different European supervisor, produced well below their maximum with a large scatter about the lower mean for the gang. At weekly intervals the two gangs were interchanged between the two stopes, with the European supervisors remaining in their respective stopes, and at the end of seven weeks of interchange both gangs were producing at near maximum level. When the interchange was stopped and both gangs returned to their original supervisors the mean performance of the gangs returned to their original levels. The effect of good quality leadership on men performing manual work is thus shown to increase the levels of performance of all the members of the gang towards...

A study was made of the physiological reactions to heat of samples of Australian aborigines and Australian Caucasians in the hot, humid tropics. Their results were then compared with those of unacclimatized and acclimatized Caucasians (South Africa). The Australian shows signs of a partial degree of acclimatization in that his heart rate and rectal temperature are lower and his sweat rate is higher than those of the unacclimatized South African Caucasian. The aborigine presents a less clear picture in that his rectal temperature is lower but his heart rate and sweat rate is the same as the unacclimatized Caucasian. A striking difference between the Caucasians and aborigines in Australia is the much higher sweat rates of the Caucasians. The lower sweat rates of the aborigine might result from the morphological feature of a greater surface area: mass ratio whereby he loses heat by radiation and convection more adequately than the Caucasian and therefore is able to conserve sweat; alternatively, he appears to have a more sensitively adjusted thermoregulatory control channel between rectal temperature and sweat rate. acclimatization to heat in northern Australia; adaptation to heat of aborigines; Caucasians and aborigines in Australian tropics; heat reactions in the tropics; morphology and adaptation to heat Submitted on February 28, 1964

The premises upon which simple methods for estimating an individual's maximum oxygen intake are based have boon tested. These premises are : (a) that heart rate and oxygen intake are linear functions of each other throughout the entire range of work up to the individual's maximum ; (b) that oxygen intake of the individual deviates very little from the mean straight line relating oxygon intake and rate of work for the population, so that the oxygon intake for a task performed against gravity can be estimated with reasonable precision from the rate of work ; and (c) that the individual variability of maximum heart rate round the mean for the population is sufficiently small to use the moan in a routine test procedure without the introduction of largo errors. Premises (b) and (c) are fully substantiated by the results reported here, Premise (a) is not strictly valid, as there is a bias of the order of 03 1. oxygon/min in the straight line relating heart rate and oxygen intake at high levels of work in most i...

A study has been made of the cold adaptation of Kalahari Bushmen under natural conditions at an air temperature of 10°–12°C. A completely ‘wild’ Bushman had a fall in total heat content, measured b...

The management of the mine at Mount Isa, Queensland, Australia decided to enquire into the following questions with regard to men working underground in hot conditions: ( a ) Which of the various heat stress indices predicts most accurately the effects on workmen of the various heat stress factors which occur in the mine at Mount Isa? ( b ) How best should the limits of heat stress be judged at which the normal 8-hour shift should be reduced to a 6-hour shift, or at which work should be stopped? With these objects in mind, oral temperatures were measured on 86 workmen after three hours of ordinary work in the mine and also on 36 occasions on 29 volunteers after three hours of stepping on and off a stool at a work rate of 1,560 ft. lb./min. These men were studied in different environmental heat stresses over the range that occurs in the mine. Dry bulb air temperatures (D.B.), wet bulb temperatures (W.B.), velocity of air movements, and globe temperatures (G.T.) were measured in the micro-climate in which each man worked. An estimate was made of the work rate of the 86 workmen. From these estimates and measurements, the predicted 4-hourly sweat rate (P 4 SR) and corrected effective temperature (C.E.T.) values were determined for each heat stress condition. P 4 SR values varied between 0·9 and 6·5 and C.E.T. between 70° and 95°F. Correlation coefficients were calculated between oral temperatures and W.B.s, C.E.T.s, and P 4 SRs and are 0·51, 0·64, and 0·75 respectively. Further analysis was confined to C.E.T. and P 4 SR. Plots of oral temperature on P 4 SR for conditions where G.T. was more than 10°F. above D.B. were found to fall well below the rest of the plots, indicating that P 4 SR exaggerates the effect of mean radiant temperature. These data were therefore excluded from the rest of the analysis. Regression equations were calculated for oral temperature on P 4 SR and for oral temperature on C.E.T. for ( a ) men `on the job9, for (i) conditions where D.B. was more than 10°F. above W.B. and (ii) for conditions where D.B. was less than 10°F. above W.B., and ( b ) for men `stepping9. This analysis showed that one overall regression line can be used for all three conditions for oral temperature on P 4 SR, but for oral temperature on C.E.T. at least two different regression lines would be needed. Also the correlation coefficients between oral temperature and P 4 SR were generally higher than between oral temperature and C.E.T. For the prediction of oral temperature in the mine at Mount Isa the P 4 SR index is to be preferred to the C.E.T. scale. These results indicate that the emphasis given to G.T. in the P 4 SR index is too great. A multi-variance analysis of the P 4 SR index shows that, in the middle of the range of heat stress conditions examined, a unit change in P 4 SR would be obtained by about the same change in W.B. and G.T. This is at variance with the present results and also with the experimental findings of the M.R.C. Climatic Physiology Unit at Singapore. It appears, therefore, that the P 4 SR index should be revised in this regard. When it came to setting limits of heat stress for a 6-hour shift and for `stop-work9, it was decided to base the limit for the 6-hour shift on a 1:100 probability of men reaching an oral temperature of 100·5°F. (rectal temperature of 101·5°F.) and to base the `stop work9 limit on a 1:2,000 probability of reaching an oral temperature of 101·5°F. (rectal temperature of 102·5°F.). The reasons for this choice of physiological criteria are given in full in the paper. P 4 SR values at which these limits are reached were determined by calculating 1:100 and 1:2,000 probability belts to the overall regression line of oral temperature on P 4 SR. The P 4 SR value at the intersection of the 1:100 probability limit and the oral temperature of 100·5°F. is 3·8 and the P 4 SR value at the intersection of the 1:2,000 probability limit and the oral temperature of 101·5°F. is 5·0. These then are the limits of heat stress in the mine at Mount Isa for a 6-hour shift and for `stop-work9. A simple graphical method has been developed and is in use in the mine for determining when the level of work and environmental heat stress have reached either a P 4 SR value of 3·8, when the shift is reduced to six hours; or, when the heat stress has reached a P 4 SR value of 5·0, when work is stopped.

Two nude resting men were exposed for two-hour periods to each of 25 dry environments, with air temperatures ranging between 12.8° C and 49.1° C and wind speeds between 0.67 m/sec and 4.94 m/sec. The mean radiant temperature of the surroundings was kept equal to the air temperature. Rates of radiant and convective heat exchange were measured directly, separately and continuously. The men had reached a thermal steady state after 105 min in the warm environments, but not in the cold environments. Graphs are presented to show the effect of ambient temperature and wind speed on the radiation and convection rates attained after 105 min, as well as on metabolic rate, sweat evaporation rate, rectal temperature and mean skin temperature. These graphs revealed some important aspects of the behaviour of man's thermal control system. In particular the physiological conductance increased with increasing ambient temperature and then “saturated” at an ambient temperature near 35° C. This saturation resulted in a constant difference between rectal temperature and mean skin temperature irrespective of the environmental conditions.

Day and night comfort votes were recorded from Caucasian residents at Weipa, a mission station in the hot humid tropics of North Queensland, Australia. The limit of day comfort for more than 50% of the men was 81·5°F. (27·5°C.) “normal” corrected effective temperature; the night limit was 78·0°F. (25·5°C.). Day comfort limits correlated well with air conditions at which sweat was apparent: night limits correlated with the amount of bed covering. Evidence of a change over 14 days in day comfort limit was found. Limitations in the effective temperature scale for expressing the “oppressive nature” of night air conditions are pointed out. Criticism is voiced of the use of dry bulb temperature instead of the effective temperature scale in conditions of high wet bulb temperatures with high relative humidity, such as in the hot humid tropics.

An attempt is made to relate the level of exercise at which disability occurs in cardiac patients with known oxygen consumption figures for various tasks. The limit to the maximum level of exercise in some patients with rheumatic heart disease is set by circulatory parameters, as in normal subjects, in others it is set by the excessive ventilatory cost of exercise.

23 Bantu male subjects were studied at various levels of work on a bicycle ergometer in order to establish the level of oxygen consumption, as a percentage of their maxima, at which laotate and “excess lactate” started to increase in the blood.

A regression line relating oxygen consumption to rate of work has been calculated on 88 men from pairs of oxygen consumption and work-rate measurements at four different levels of work. A regression line has also been calculated for maximum oxygen intake against gross body weight for 338 men. From these regression lines it is possible to estimate the proportions of their maximum oxygen intakes a light and a heavy man would use in stepping on and off a 1 ft stool at 6, 12 and 24 times per minute. The slopes of the lines are such that both men would use similar proportions of their maximum oxygen intakes at each of the three rates of stepping ; the percentages are 26 per cent, 36 per cent and 55 per cent respectively. The distribution of the gross body weights of the 338 men has been used to calculate a body weight such that 95 per cent of the men having weights above this value would have maximum oxygen intakes of 2-0 litres/min and more and therefore be capable of a moderate rate of work. A gross body wei...

Sweat rates and rectal temperatures were measured hourly in two sets of 4 hour experiments. In one set, the men worked at a constant rate of 1560 ft. lbs/min requiring an oxygen consumption of 1.0 litre/ min (i.e. a metabolic rate of 5 Cal/min), at four different levels of heat stress, i.e., 87, 90, 93 and 96°F Effective Temperature on different days. In the other, the environmental heat stress was kept constant at 90° F Effective Temperature and the subjects worked at four different levels of work, each on a different day. The sweat rate/rectal temperature relationships, both on an hourly basis and as an average of the 4 hours of exposure, were closely similar in these two experiments. From this fact it is concluded that the increase in core temperature is the main factor controlling the rate of sweating. The curves relating sweat rate to rectal temperature were a little higher in the experiment in which the work rate was increased, indicating that muscular exercise has a specific and small effect on the sweat rate, apart from its influence on the core temperature. The curves fitted to sweat rate against rectal temperature showed the characteristic “sensitive” zone, i.e., a rapid rise in sweat rate with increase in rectal temperature between 98.2 to 101.0 ° F and a zone of “saturation” of the control channel, i.e., sweat rate reached a maximum value when rectal temperature rose above 101.0 ° F.

RQ, plasma insulin, blood glucose, lactate and pyruvate were measured in six fit, normal subjects during a series of exercise and rest experiments with and without sucrose ingestion. Subjects exercised on a bicycle ergometer for 50 min of every hour for 6 h at about 47% of the group's average maximal aerobic capacity. In the resting experiments, the subjects sat for 6 h in an armchair. A solution containing 100 g of sucrose was ingested at the beginning of the fourth hour during the sucrose experiments. Ingestion of sucrose caused a significant increase in RQ, plasma insulin, blood glucose, lactate and pyruvate in both exercise and rest experiments. Insulin, lactate and pyruvate concentrations rose higher during rest after sucrose ingestion than during exercise. The time courses of the changes in RQ, insulin, glucose, lactate and pyruvate after sucrose ingestion, suggest that glucose entering the cell during rest is immediately oxidized, while during work there is some delay in the oxidation of glucose.

The concentration of lactate and pyruvate was determined in the blood of 13 subjects at three aerobic and four anaerobic levels of work before and after a period of training on a constant work-rate bicycle ergometer. In addition each man's maximum oxygen intake was established on either the bicycle ergometer or the motor-driven treadmill, by means of the Douglas bag technique, before and after the period of training. The results obtained demonstrated that a regime of training influenced the maximum oxygen intake and also the level of oxygen intake at which “excess lactate” starts to appear in the blood. During the training of the subjects these two physiological parameters changed independently of each other but large individual differences were also observed. The mean maximum oxygen intake of the men, which was 2.888l/min before training, increased to 3.060l/min (a change of 7 per cent) after the men had trained for a period of 4 to 16 weeks. During this period of training the mean level of oxygen intake, expressed as a percentage of the maximum value, at which “excess lactate” appeared increased from 46 to 62 per cent. The relationship between the degree of fitness and the appearance of anaerobic metabolism during work is discussed. In untrained individuals the onset of anaerobic metabolism occurred at 40–45 per cent of the maximum oxygen intake, in trained individuals at 55–60 per cent and in the exceptionally well-trained men at about 70 per cent.

Oxygen consumptions were measured at various levels of work up to the individual's maximum. At submaximal work they were significantly lower in heat than in comfortable temperatures, but maximum oxygen intakes were not significantly different. In comfortable conditions cardiac output and A-V difference both contributed to rise in oxygen intake during submaximal work. At maximal effort increase in arteriovenous difference accounted for the ultimate rise in oxygen intake. Both heart rate and stroke volume contributed to increase in cardiac output up to 1.0 liters/min oxygen intake; above this heart rate was the sole factor. In heat the major change in hemodynamics was an increase in heart rate with an associated fall in stroke volume. Neither cardiac output nor arteriovenous difference was significantly altered from comfortable conditions. “Excess” lactate occurred at significantly lower levels of work in heat than in comfortable conditions. Working muscles were therefore relatively more anoxic in heat at submaximal work, and this accounted for lower oxygen intakes. At maximal work the degree of anoxia was the same in both temperature conditions. Submitted on August 22, 1961

Bushmen in the Kalahari desert fulfill two criteria for acclimatization to heat. They exercise actively, in hunting, in relatively severe heat in midsummer. Compared with unacclimatized Bantu they have higher sweat rates per square meter and lower heart rates. However, rectal temperatures are not much lower than those of unacclimatized Bantu. River Bushmen present a paradoxical picture. In summer sweat rates are higher than in winter, but are not as high as desert Bushmen. Summer heart rates are, however, higher than in winter. Rectal temperatures in the two seasons are similar. The higher sweat rates in summer are good evidence of better acclimatization than in winter; the higher heart rates may be a reflection of differences in physical fitness in the two seasons. association of morphology and metabolism on cold exposure; cold responses of Bantu, Bushmen, and Caucasians; heat conductance and skinfold thickness in cold; metabolisms of Bantu, Bushmen, and Caucasians in cold; toe, finger, and rectal temperatures of different ethnic groups in cold Submitted on February 4, 1964

Maximum oxygen intakes, heights, weights and skinfold thicknesses were measured on 106 Bantu male recruits to the gold mines. Three different tribes from different parts of Africa were represented in the sample. Regression equations were calculated for the relationships between maximum oxygen intakes and 1. gross body weights, 2. gross body weights and heights, and 3. gross body weights, heights and per cent body fat. Residual mean squares were also calculated. From these results it can be estimated that 27 per cent of the variations between individuals in maximum oxygen intakes can be accounted for by their differences in gross body weight and a further 3 per cent by differences in height (weight is positively correlated and height negatively correlated with maximum oxygen intake). Excluding the effect of differences in per cent body fat does not alter the residual mean square so that none of the variations between individuals in maximum oxygen intake can be attributed to this factor. Treating the tribal groups separately also did not reduce the residual mean squares of any of the three tribes. Of the factors measured in this experiment only differences in weight and height in the Bantu contribute to the variations between individuals in maximum oxygen intake and 70 per cent of the variations is left unaccounted for.

To be able to predict man's thermal response to any given environment it is essential to have a thorough understanding of man's thermo-regulatory mechanism. The mechanism is dependant on a number of highly non-linear variables. An analogue computer can be of great value with such a problem as non-linear control characteristics are easily incorporated into its programme. The computer is used as a model to reproduce man's thermal behaviour. This paper describes the application of such a computer. A number of tests were made to study some thermal control characteristics and the results are compared with those of a series of experiments performed on two resting subjects who were exposed to various environmental conditions in a climatic chamber.

In 20 African mine labourers there was a significant average gain in weight from 122 lb on recruitment to 128 lb after one month, as a, result of a stable diet and regular physical labour. The mean estimated maximum oxygen capacity rose significantly from 2·32 l to 2·79 l after one month, with a further slight rise to 2·83 l after four months. On each of the three occasions that these men were studied maximum oxygen capacity was highly correlated with gross body weight, the correlation coefficients rising from 0·59 to 0·70 after one month and to 0·83 after four months. Some exceptions to the general rule of ‘ the heavier the man the higher his oxygen capacity ’ are discussed. The ratio of oxygen intake to rate of work did not alter significantly, indicating that the subjects did not become more efficient in the unitization of oxygen. Subjects ventilated 30 per cent more air through their lungs in order to take in one litre of oxygen per min for work at 6,000 feat altitude than do men at sea level.

Mean skin temperatures, rectal temperatures and sweat rates were measured on four highly acclimatised subjects. They were exposed for 180 min to 16 different combinations of 4 metabolic rates and 4 air temperatures, ranging from cold (10°C) to hot (49°C). Mean sweat rates for the second hour were plotted against mean rectal temperaturesfor 4 different levels of skin temperature and viceversa. These graphs indicate, firstly, that sweat rate does not increase until rectal temperature rises above a threshold value of 36.5°C; thereafter the increase in sweat rate depends upon the level of mean skin temperature, being greater the higher the mean skin temperature is. Secondly, sweat rate does not increase markedly until mean skin temperature rises above 33°C but the increase in sweat rate above 33°C depends upon the level of rectal temperature, being greater the higher the rectal temperature is. The interrelated effects upon sweat rate of mean skin temperature and core temperature can be explained by means of a relatively simple physiological system, comprising temperature sensors in the hypothalamus and skin, and a heat loss and a heat conservation integrating centre. Mathematical equations have been developed to express the relationships between sweat rate, core, and mean skin temperature for cool conditions, but these relationships are so complex that it is preferable to use an analogue computer for these purposes.

From these results it appears that a hot, humid environment can be used to study the physiological reactions of desert dwellers, and to compare them with the reactions of other populations, without introducing any significant errors.

The physiological reactions to heat of samples of French servicemen and of Arabs in the Sahara Desert, were compared with those of South African Caucasians. Both Sahara groups displayed evidence of partial acclimatization; their reactions were better than those of the unacclimatized; but not as good as those of the acclimatized South African Caucasians. The French servicemen were slightly better acclimatized than the Arabs; they had lower rectal temperatures and heart rates, and higher sweat rates. This paradoxical finding indicates that the Arabs, although their ancestors have lived in the Sahara Desert for some centuries, display no greater adaptation to hot conditions than recent Caucasian inhabitants. The morphology of the Arab gives him a greater surface area: mass ratio than the Caucasian. This favors heat loss, but under the test conditions the Arabs had no apparent advantage in physiological reactions. The differences in morphology of the Arab and Caucasian appear to be related more to their nutritional state and physical activity levels than to any structural adaptation to heat. acclimatization to heat in Sahara Desert; adaptation to heat of Arabs; Caucasians and Arabs in Sahara Desert; heat reactions in the desert; morphology and adaptation to heat Submitted on February 28, 1964

Fifty-two groups of about 20 men each were exposed for 5 hr to various combinations of work rate, environmental temperature, and wind velocity. Hourly observations were made of oxygen intake and oral and rectal temperatures. Oral/rectal temperature differences increased significantly with time only under those conditions where steady-state responses were not achieved. Increasing wind velocity from 50 to 400 cm/sec, raising air temperatures from 27 to 36 C, and combinations of these factors had no significant influence on the difference between the recorded temperatures. The main contributing factor to oral/rectal temperature difference is work rate. Increasing energy consumption from 2.5 to 9.0 Cal/min resulted in a rectilinear increase in average difference from 0.5 to 1.1 C. A warning is expressed against the indiscriminate use of oral temperatures in work and heat studies influence of work and heat stress on oral/rectal temperature differences; oral versus rectal temperatures Submitted on May 18, 1964

Incapacitation of men due to heat has been a hazard for many years in hot industries and in military operations in the tropics. Measures to combat the adverse effects of heat on man have taken two directions. One approach has been to set limits to the rate of work when the air conditions exceed a certain critical level

Heat reactions of 20 Caucasian and 22 Bantu males were compared, first in the unacclimatized state and then in the acclimatized state. The study was conducted at temperatures of 90 F wet-bulb and 93 F dry-bulb at a work rate of 1 liter O2/min consumption. The performances of the unacclimatized Bantu were superior to those of the Caucasians. All 22 Bantu completed the 4-hr experiment, while 10 Caucasians failed. The mean rectal temperature of the Bantu was significantly lower than that of the Caucasians, but not the mean heart rate and mean sweat rate. When both groups were highly acclimatized all men from both groups completed the 4-hr experiment, and their reactions to heat were significantly different from their reactions in the unacclimatized state. Sweat rates, particularly, increased very much. The differences between the two highly acclimatized groups in rectal temperatures, heart rates, and sweat rates (except the 4th hr) were not significant. Although superior in the unacclimatized state, the Bantu does not appear to have an inherent advantage in the ability to regulate the body temperature. Caucasians versus Bantu in reactions to heat; physiological reactions in exposure to heat Submitted on August 19, 1963

An examination is made of the relationship between the energy expenditure in litres of oxygen consumed per minute, as measured by the physiologist, and the performance index, as assessed by the work-study engineer. The data used in the analysis were obtained from 16 Bantu labourers engaged in shovelling sand at four different rates of work into a mine car of 1 ton capacity. A close relationship between mean oxygen consumption and mean performance index over the range of work levels was found. A linear model appeared to describe the relationship between these two variables adequately. The particular linear relationship between the variables was, however, dependent on the observer, i.e. the lines for the two work-study engineers were different from each other. A performance index value of about 75 was found to be equivalent to an oxygen consumption of about 1-5 litres per minute. This is 50 per cent of the average Bantu mine labourer's maximum oxygen intake and, on physiological grounds, this is the rate of...