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Data on the morphological development of inbred and F1 hybrid mice reared at 22·8 °C dry bulb, 17·8 °C wet bulb, and 32·2 °C dry bulb, 26·7 °C wet bulb are presented. Animals were weighed at birth, 1 and 2 weeks of age and at each developmental stage. All animals were examined for the freeing of the ear pinnae, eruption of the lower incisor teeth and perforation of the eye membranes and in addition females were examined for the appearance of the first pair of nipples and for perforation of the outer part of the vagina. Within each environment, but especially at 23 °C, there are genotypically characteristic differences in the ages at maturation of each variable. Though the ages of maturation of the different variables are highly correlated within genotypes, early maturation of one variable is not necessarily associated with the early maturation of others. Reciprocal F1 hybrid differences indicate a maternal effect upon the age of maturation which is more marked at 23 than at 32 °C. Comparisons of the ages at maturation in the two environments showed that the only character to mature earlier at 23 than at 32 °C was pinna freeing. The most marked influence of the 32 °C environment in advancing development was on the appearance of nipples and on vaginal opening. In almost all cases, animals reared at 32 °C were lighter at the time of maturation than those at 23 °C. Hence when allowance was made for environmental differences in body weight the association between an environment at 32 °C and early development was further enhanced. Those animals that were relatively heavy when weighed at the weekly interval prior to maturation matured earlier than the lighter ones, especially at 23 1C, indicating that morphological maturation was closely related to overall growth. Both the within, and between, litter variation in the ages and body weights at maturation of a strain tended to be greater in animals exposed to the higher temperature. In bilaterally distributed characters, asymmetrical maturation was more common at 32 than at 23 °C.

1. The dietary intake, and urinary, cutaneous and faecal loss of water, sodium, potassium and iron have been studied in young men living and performing moderate work in a hot climate. The dietary intakes of K and Fe were lowered during part of the study.2. The subjects were already somewhat acclimatized to heat; further acclimatization was achieved when they were performing work, and this was assessed in terms of the increase in their rate of sweating.3. The subjects tended to be in marginally negative Na balance, partly owing to lowered Na intakes. Intakes and outputs of K were in balance. Losses of K in sweat amounted to 15% of intake when the dietary level was reduced.4. The subjects were slow in adapting to changes in Fe intake, 8 d being an insufficient period for adaptation after their intake had been halved. Losses of Fe in sweat were approximately 0·3 mg/d, or one-third of the estimated requirement for absorbed Fe.5. It is concluded that Fe losses in sweat could be a significant factor in Fe depletion if dietary Fe was low or unavailable, as there was no evidence that a low intake and absorption affected sweat losses.

The necessity for an adequate salt intake for people working in hot climates has been recognized for a long time (Moss, 1923). Salt deficiency is with some certainty known to cause heat cramps (Talbott, 1935 ; McCance, 1936 ; Ladell, 1949) and is very likely the cause of lesser degrees of ill health and inefficiency (Taylor, Henschel, Mickelsen, and Keys, 1943 ; Ladell, Waterlow, and Hudson, 1944). To understand how such ill-effects arise, it is obviously necessary to establish the changes in salt metabolism associated with sweating at high temperatures. In reviews of this matter Ladell (1945) and Robinson (1949) have pointed to the confusion in the literature regarding the exact effects of dietary chloride and acclimatization on the chloride content of the sweat. The recent experi ments of Conn and Johnston (1944; Conn, Johnston, and Louis, 1946) have thrown much light on this problem. This work indicates that when the salt loss during exposure to heat is greater than the dietary supply, the " negative " balance may only be temporary ; a restriction in both sweat and urine chloride output takes place so that after some days the salt deficit is made good and the total salt output is readjusted to the level of intake. Conn's work is important in showing that balance is possible at levels of salt intake even as low as 6 g. per day for men sweating 5-6 kg. a day. Unfortunately, this, as well as earlier work, may give the impression that this restriction in salt loss is necessarily or invariably a part of the process of acclimatization to heat, whereas in logical extension of Conn's findings one would expect no decrease in sweat chloride on a sufficiently high salt intake. The sweat chloride content on higher salt diets during the acclimatization period seems not as yet to have been investigated in experiments like those of Conn in which the subjects lived continuously in the heat. In the earlier work of Black, McCance, and Young (1944), h wever, in which recumbent individuals were exposed daily for short periods in a radiant heat bath, a decrease in sweat chloride output did not, in fact, occur on a high salt diet whereas on a low level of intake a decrease took place. Th experiments reported in this paper are similar to those of McCance (1936) and Black, McCance, and Young (1944), in that they involve short periods of exposure to heat. They were carried out on working subjects exposed to strictly standardized condi ions of work. When this investigation was nearly completed, papers by Robinson, Kincaid> an Rhamy (1950) appeared in which they reported results with which those of the present experiments are in substantial accord. It seems useful to ecord our results, for in addition to confirmation of an important physiological response to hot climates, they are concerned also with ano her aspect of this problem. In our experiments chlorid analysis was made not only of the body swe t from the general body surface but also on sweat collected in arm bags. The difference in the composition between the sweat from these two collections helps to explain some of the confusion referred to by Robinson (1949) and Ladel (1945). Finally, a separate series of ex periments on unacclimatized persons is presented because of its bearing on the " salt conserving " responses of the body at high temperatures.

Four inbred strains of mice and theF1hybrids between them have been reared from 3 to 16 weeks of age at 70 °F (d.b.), 61 °F (w.b.) (control-reared) and 90 °F (d.b.), 85 °F (w.b.) (heat-reared), using a split-litter experimental design. It is shown that growth in body weight is in part determined by environmental temperature. The weight of young heat-reared mice usually increases more rapidly than that of their control-reared litter-mates but at later ages, particularly during the maturation period, the latter typically grow more rapidly. The magnitude and direction of the environmentally determined responses is dependent upon the genotype of the animals. The growth of the F1hybrids in the two environments is more similar than the growth of the inbreds from which they were derived, and the differences in the responses of the various hybrids are smaller than the corresponding inbred differences. To some extent, however, the response of a hybrid can be predicted from the responses of its inbred parents. The variability in weight of heat-reared animals is usually smaller than that of control-reared ones. The variabilities of the two environmental forms show the greatest difference soon after the animals are separated, but they become more similar with increasing age; in some genotypes the variation between the heat-reared animals may ultimately exceed that of the control-reared ones. There is a correspondence between the growth rate and the variance and it is concluded that both reflect the optimality of the environment: a rapid growth rate and a low variation indicating a favourable temperature. Heterozygotes in any one environment usually have a smaller variability than homozygotes and this is indicative of their greater homeostasis, but the similarity of one of the inbreds to the hybrids in weight variance behaviour and weight responses shows that a marked reduction in somatic fitness is not an inevitable consequence of inbreeding.

1. The effects of blocking agents on the responsiveness of the cast' pad and human forearm sweat glands have been studied. 2. Of the anti-adrenergic substances examined (dibenamine, phenoxybenzamine, bretylium, guanethidine and phentolamine) only high doses of guanethidine and phentolamine produced any consistent and significant measure of blockade, and small doses of atropine were as effective as these large doses of guanethidine or phentolamine. 3. It is concluded from the blockade of chemical stimulation as well as transmission by these substances that (1) there are only cholinergic fibres innervating eccrine sweat glands, and (2) any inhibitory action by anti-adrenergic substances is due to interaction with cholinergic receptors in the glands.

SUMMARY The output of urinary adrenocorticoids has been studied in man before, during and immediately after exposure to high environmental temperatures. The results indicate that while there was no significant change in the excretion of 17-hydroxycorticoids, cortisone and cortisol or of tetrahydrocortisone and tetrahydrocortisol there was a significant increase in the output of aldosterone.

Two inbred strains of mice and theF1hybrid between them have been reared from 3 to 12 weeks of age in a fluctuating temperature environment. The environment was characterized by temperatures of 90 °F (d.b.) 85 °F (w.b.) and 70 °F (d.b.) 61 °F (w.b.) for the same length of time each day. Mathematical curves of the formy = a + brxhave been fitted to body weight and tail length growth. It is shown that in both characters the hybrids display a greater adult size, a more rapid growth and a superior canalization of growth than the inbreds from which they were derived. When the growth in the fluctuating environment is compared with that, previously described, in corresponding constant temperature environments, i.e. either 90 °F (d.b.) 85 °F (w.b.) (heat) or 70 °F (d.b.) 61 °F (w.b.) (control) it is found that hybrid luxuriance is most manifest in constant heat. However, in these conditions, the inbreds tend to disperse their growth rate relatively more rapidly than they do in the other environments. It is also shown that growth in the fluctuating environment is not strictly intermediate between growth in the constant conditions, but much more closely resembles growth in the heat than in the control.

It is probably no exaggeration to say that for not a few archaeologists the examination of skeletal remains means the measurement of the cranium with the object I of establishing ‘ race ’. Indeed there may still be some who believe (or who have been led to believe) that the physical anthropologist can with confidence diagnose the ‘ race ’ or even ‘ subrace ’ of a single skull. What is perhaps worse is the idea that race allocation represents the entire potential biological interest of skeletal material or the sole activity of the physical anthropologist. These views are happily not so prevalent as they were not long since. There is a better appreciation of the scope of physical anthropology and of its greater concern with the general biology of human communities, their genetics and ecology-an approach which is necessary if the maximum biological information bearing on the life of extinct groups is to be extracted from the refractory material offered by skeletal remains. Human bones and teeth often give some insight into the conditions of life affecting the community as well as (sometimes) an indication of the origin and affinities of the group. For the skeleton is susceptible to modification both by the action of environmental agencies and by genetic factors. It is known, for example, that identical twins reared in different environments vary more in such ‘ classical ’ measurements as head length, head breadth and cephalic index, than do twins brought up in the same environment (Newman, 1940). The effect of change of environment in altering the head and body shape of descendants of immigrants has been demonstrated also by Shapiro (1939) and Lasker (1946) much more convincingly than was done in Franz Boas’ pioneer investigation which was subsequently criticised by Morant and Samson (1926). But much more work is clearly necessary before a genetic analysis of such polygenic characters as bone size and shape becomes available and we may hope that the current interest in studies of growth and physique in the living will provide the necessary information.

THE occupancy of air raid shelters presents, actually or potentially, many of the whole range of problems with which the practice of ventilation is concerned. The term ‘ventilation’ is here used to include heating and other air-treatment; it may be defined as ‘the provision of air hygienically and physiologically adequate in quantity and quality’. In air raid shelters conditions arise which tend to reduce the efficiency of ventilation very considerably. While on one hand, the supply of air is hampered in a number of ways by safety requirements, the demand tends at the same time to be greatly increased. Structural alterations to places used as air raid shelters usually require the blocking or baffling of the natural airways; lighting restrictions interfere further with ventilating arrangements; the danger of gas attack may reduce the available air supply merely to the air capacity of the shelter. The fitting of ventilating appliances may entail some structural weakening of a refuge; and the dependence of most large plants on outside power is also a potential source of weakness. Furthermore, since in shelters the ordinary density of living-room occupancy is much exceeded, satisfactory standards of ventilation are distinctly more difficult of attainment.

The main object of the present trials was to ascertain whether ill effects attributable to cordite could be reproduced experimentally. Additional aims were to obtain information on (1) the mode of absorption of cordite, (2) the influence of cordite fumes on the efficiency of operatives at ambient and at high wet-bulb temperatures, (3j the occurrence of any acquired immunity, (4) the extent, if any, to which carbon dioxide might contribute to the symp toms, and (5) the concentration of nitrogen dioxide and carbon monoxide released during cordite handling in addition to the vapour of nitroglycerine.

DURING August–September 1958, an expedition organized by the Kalahari Committee of the University of the Witwatersrand (in which the Anthropology Laboratory of the Department of Human Anatomy, Oxford, participated) carried out anthropological, medical, dental and other investigations on Bushmen in the Central Kalahari. The anthropological interest of this study lies in the following: (a) two communities examined, some 70 miles south of Ghanzi, were living a primitive hunting and food-gathering existence and could be compared with a third group of Bushmen living on farms in the Ghanzi district; (b) the blood of Bushmen from the Kalahari region has not previously been grouped; hitherto all such data have been obtained from Bushmen of South-West Africa; (c) the antigens tested included the recently discovered Diego (the serum was kindly supplied by Dr. Layrisse) and also V and Js (sera kindly supplied by Dr. Eloise Giblett). Tests with anti-Diego sera were particularly apposite since some anthropologists have considered it possible that the Bushmen (and Hottentots), on account of their skin colour and frequent possession of an internal epicanthic fold, incorporate a Mongoloid component of distant or even recent derivation. There also is still uncertainty on the exact affinity of the Bushmen to existing Negroid populations. The V and Js antigens are common in Negro populations and therefore supplement information on Negro affinities afforded by other blood-group systems.

The testicular artery in mammals convolutes to a variable extent before reaching the testis, and is closely surrounded by the veins of the pampiniform plexus. Evidence is presented suggesting that this vascular mechanism has a thermoregulatory function for the testis. Species differences in the degree of convolution and calibre of the testicular artery and its relation to the veins of the pampiniform plexus would appear to account in some measure for observed differences in abdomino-testicular temperature gradient. Experiments on dogs, rams, and goats also indicate that the close relation of the pampiniform plexus of veins to the testicular artery is well adapted to bringing about preheating or precooling of arterial blood flow to the testis. We are indebted to Prof. H. C. Bazett for the method of soldering the thermocouples and gifts of plastic tubing, and for his interest in the initial stages of these experiments. We also wish to thank the late Dr A. E. Barclay for his help with the radiography in this investigation.

Nicol, J. F., Dore, C., Weiner, J. S., Lee, D. E., Prestidge, S. P., and Andrews, M. J. (1973).British Journal of Industrial Medicine,30, 325-334. Comfort studies of rail passengers. A short series of trials is described in which a specimen car of the new High Density Rolling Stock was laden with passengers at different densities and under different environmental constraints, designed to simulate `shut-down' conditions. The results suggest that the limit for comfort, 21·8°C corrected effective temperature (CET), proposed by Bell and Watts (1971) is reasonable but that temperatures some 3 or 4°C higher can be tolerated without undue discomfort. The physiological limit for safety recommended by Bell and Watts is a CET of 30·6°C. This will be reached in less than 20 minutes if there is a power failure in warm conditions in crowded trains. An undesirable, possibly dangerous, level of discomfort will be experienced by passengers in ventilated but crowded trains after 30 minutes. In any case it is recommended that the globe temperature in a carriage should not exceed 30°C.

1. The influence of repeatedly raising the body temperature by radiant heat to a level at which acclimatization to heat is normally acquired was investigated in two series of experiments, the first without the subjects sweating, the second with sweating. 2. In a second investigation local sweat-gland activity was induced by drug injections on successive days without raising the body temperature. 3. These experiments show that the increased sweating capacity characteristic of acclimatization to heat is a result of sweat-gland activity and does not appear to be induced by or to depend on an elevated body temperature. 4. Secretory activity results in a loss of glycogen from sweat-gland cells on the first day of heat exposure but not after the glands have been ‘trained’ by acclimatization to heat. 5. The state of acclimatization has no influence on the threshold concentration of acetylcholine required to elicit sweating when injected intradermally.