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Taxonomic survivorship curves may reflect stratigraphic as well as biologic factors. The approximately lognormal distribution of lengths of Phanerozoic time intervals produces an error in the estimation of taxonomic durations that is also lognormally distributed. As demonstrated by several simulated examples, this error may cause concave taxonomic survivorship curves to appear linear, especially if the maximum durations involved are relatively short. The error of estimation also makes highly concave taxonomic survivorship curves virtually unrecognizable. Incomplete sampling of the fossil record, on the other hand, may not be a serious problem in survivorship analysis. Simulated paleontological sampling employing a simple model suggests that survivorship curves tend to retain their original shapes even when as few as 20% of the taxa have been discovered. However, concave taxonomic survivorship curves tend to lose their concavity as efficiency of sampling declines.

Mastectomy may disrupt a woman's sex life if she believes the disfiguring surgery has left her sexually unacceptable and/or inadequate. Her perception of her postoperative sexual adequacy and desirability depends on biologic factors such as pain in the operative area; psychologic factors such as her perception of her partner's reaction; social factors such as societal standards of sexual desirability. If the nurse knows the patient's feelings about each of these factors, she can perhaps predict how the woman will adapt sexually in the short and long runs and refer her as needed for sexual counseling to forestall sexual problems.

I T IS generally conceived that the success of orthodontic therapy depends not only on the digital skill of the operator but also on a thorough knowledge of the mechanical principles of treatment and of the biologic laws which form a common basis of dental and medical practice. A failure to recognize and apply some of these fundamentals may lead to undesired results and render the prognosis unfavorable. To complicate the problem further it must be admitted that the etiology of a large number of tissue changes in the paradentium is only partially understood. Probably for this reason it happened that a prominent member of your profession stated more than ten years ago that the results in a certain percentage of his cases were not as favorable as desired because the patients had been originally, as he termed it, “poor risks.” This alibi may be perfectly legitimate ; however, it should be remembered that cases may still be risky even if they are “good risks.” If we consider the definition of the word “risk,” we realize that it means a chance of encountering harm or peril ; it means hazard or danger, as in “the risk of drowning. “i In relation to orthodontic therapy or prognosis the word “risk” implies that we are uncertain, to say the least, as to the efficacy of many therapeutic methods and the use of this term by orthodontists is an admission that certain fundamentals are not yet understood. Many obscure factors (frequently of a biologic nature) may interfere with local therapy‘s0 that the effects of mechanical appliances are not those that were planned and desired. During the past few decades, orthodontic science has progressed largely through improvement of mechanical appliances for the correction of dentofacial anomalies. Little progress has been made in discovering etiological factors responsible for early malposition of teeth or biologic factors affecting the tissue unfavorably during orthodontic movement of the teeth. When I appeared before your society three years ago in New York, I reported4 that a large percentage of orthodontic patients who had marked root resorptions were found to have coexistent systemic disturbances. In another group of patients who also had root resorptions but never received orthodontic treatment because of a favorable occlusal relationship, about the same frequency of systemic disturbances was found. Emphasis was placed on the fact

Attempts to determine the biologic factors which govern natural immunity to bacterial infection have too often been attempts to reduce the mechanism of resistance to terms of a single factor. Thus, only after an extended epoch of controversy between two schools, each seeking to explain natural immunity in terms of a single general factor, namely, body cells in the one instance and body fluids in the other, have we come to recognize, as, for instance, in the role of opsonins, the dependence of each of these factors on the other and the fallacy of attempting to eliminate either. In those instances, also, in which a relatively high or low body temperature has been advanced as the basis of resistance, the tendency has been to emphasize this single feature to the exclusion of other factors.

1. 1. The problemof radiotherapy will not be completely solved until the biologic factors entering into this equation have been better understood and more directly controlled. 2. 2. Individualization of cancer patients is of prime importance and for this reason surgery and radiotherapy must supplement each other, and change their roles from predecessor to successor, from time to time, according to the mature judgment of the treating clinician. 3. 3. The localistic conception of cancer must be modified, and malignant disease must in the light of recent advances be considered as a gereral affection characterized by a constitutional morphologic inferiority of some tissue. 4. 4. The success of x-ray therapy in malignant disease is not wholly dependent upont the destruction of the tumor cells, but also, to a very large extent, upont the general cellular immunity of the organism, and upon a preservation and stimulation of the forces governing this immunity. 5. 5. Surgery should be given first choice whenever possible. The remoral of the main malignant focus and large metastatic deposits gives the economy a better chance to utilize its reserve of natural immunity in combating the remaining disorganized malignant stragglers, which must still be weakened by postoperative deep roentgentherapy. 6. 6. The administration of deep x-ray therapy requires training and preparation; the possession of an x-ray apparatus does not indicate therapeutic skill. From a gynecologic viewpoint, I may add that modern gynecology demands, besides a thorough preparation and mastery of surgical technic and a comprehensive understanding of the female patient in particular, also a knowledge of the main principles of radiotherapy. 7. 7. Radiotherapy must be administered by, or under the direction and colse supervision of, clinician, in order to obtain the best resutls. 8. 8. It is quite possible that some of the present day views regarding cancer therapy by means of surgery, radium, or x-rays, will undergo may changes. One thing, however, is certain, that the x-rays as one of the most important weapons in combating deep seated malignant foci will never diseappear from our medical armamentarium.

AS long as the assumption is valid in most cases that carcinoma is, in its onset, a localized disease, eradication of the local lesion should provide cure. And this, irrespective of disturbing biologic factors beyond understanding and control, justifies the endeavor for early diagnosis. In the field of bronchial carcinoma x-ray diagnosis has been leading for the past few decades, only occasionally overtaken by bronchoscopy. In the past, the mistakes were usually those of interpretation rather than errors of discovery. In fact, it is a common occurrence that, in a roentgenogram of the chest taken as a routine procedure, a . . .

T HE LIMITED success that has so far been achieved with heart transplantation in patients has raised early hopes. Still, a mood of pessimism and frustration has descended upon many because of the apparently unpredictable outcome of this logistically complex and expensive effort, which may be considered of questionable public health value. I believe that heart transplantation will gradually take a rightful place in the treatment of certain cardiac disorders and will take this position in the present brief summary of some of the biologic factors bearing upon the future of this procedure.

Summary An attempt has been made to point to some of the emotional factors encountered in studying a group of patients presenting difficulties in adjusting to dentures. Two general types of difficulties with dentures were presented clinically. The first of these manifested itself in the inability to tolerate dentures, even though careful examination ruled out mechanical and biologic factors. In each of these, the gag reflex was stimulated giving rise to “psychologic gagging.” In the other group, the patients neglected to seek service to imperfectly constructed dentures until serious tissue damage resulted. Evidence from the life histories and psychologic examinations of this group seemed to reveal consistently the use of denial by the personality and was especially brought to light in their apparent refusal to accept the condition. It was suggested that the manner in which an individual views the loss of his original teeth will in part influence how he will adjust to his prosthesis. Those patients who could not adjust to dentures were found to be acutely aware of their loss and the implications, while in the other group, a strong attempt at denial of the loss was evident. Other factors influencing the success of the treatment process were pointed out. These mainly centered about the relationship between the dentist and the patient, and the importance of recognizing these factors was stressed. The attitudes which the patient brings to the dental office, the dental situation itself, and the dentist's own personality, all were found to enter into the success of the total treatment attempt. While these studies have been largely exploratory in nature, it has been amply demonstrated that the patient must be viewed as a total functioning unit. The treatment setting in which he is placed and the interrelationships between patient, dentist, and the over-all environment must be carefully evaluated. Further combined efforts using this approach studying other syndromes should aid considerably in establishing more adequate diagnostic skills in treatment of denture problems.

The occupational hygiene survey is a technic for the evaluation of the working environment and its effects on the health of the workers. The three basic components of the vocational complex are basic environment, machine-process requirements, and biologic factors. The many facets of the survey and evaluation of the interrelations and effects of these components are discussed in detail.

Information of considerable importance has been gained from comparisons of the incidence of various malignant diseases, both between and within various populations. Although the role of hereditary factors can never be completely excluded, it is likely that the vast majority of the geographic differences observed for most cancers are environmentally induced. This would also appear to be true of the lymphomas and leukaemias, which are characterised by markedly diverse international patterns. When differences in incidence are polarised to the extent that a disease occurs only or mainly in relatively circumscribed areas, as is true with Burkitt’s lymphoma, this allows one to concentrate on the differences between regions of high and low incidence. Do these areas differ mainly with respect to their physical environment (e.g. climate, geology), biologic environment or both? It must be realised, however, that it is difficult to dissect man from his environment; just as the nutritional, hygienic and socio-economic standards set by man can alter his environment so too existing physical and biologic factors can dramatically affect his activities. Despite all its uses, geographic epidemiology has its limitations, largely due to the lack of suitable statistics from certain areas, especially more primitive ones, and under ascertainment of cases which may be a function of the diagnostic facilities available. It is therefore imperative that other methods be employed in evaluating the possibility that a disease is environmentally induced. These include time—space cluster analysis, migration studies and evaluation of peculiar situations such as familial aggregations of a disease. Again each method has its own limitations so that a variety of approaches must be taken to adequately evaluate this question. This chapter examines the evidence that environmental factors might be important in the aetiology of certain lymphoreticular disorders.

Many have made great efforts to improve the results of treatment for pulmonary metastasis. There are many problems to be solved in this field. We calculated the growth rate of a tumor based on the time interval and change in tumor size and divided the patients into two groups in relation to the tumor growth rate. We have made a study of how the growth rate of tumor influences the results of treatment in the two groups and have sought to determine what kind of treatment is most reliable for a metastatic lesion. Our study indicates that pulmonary resection is the most reliable treatment for metastatic pulmonary disease. The result of surgical treatment for a patient with a rapid tumor growth rate was inferior to that of a patient with a slow growth rate, though this result was not necessarily disappointing.

Results of inhalation exposure of guinea pigs to carbon followed by NO 2 , or to NO 2 followed by carbon, are presented to exemplify both specific and general problems inherent in using animal systems to determine injurious effects of environmental agents. Inhalation of carbon alone is followed by a macrophage response. Subsequent exposure to NO 2 results in lung destruction. Inhalation of NO 2 followed by carbon gives a macrophage response of lesser degree. These findings are interpreted to mean that the sequence of exposure may determine a given response. The limitations of this study indicate the necessity of using approaches which control or measure multiple biologic factors operative at different levels of organization of diverse animal systems.

"Environmental geology" is a term which is becoming widely used and misused. The rocks that contain fluids and through which they pass, together with the fluids themselves, physical conditions such as temperature and pressure, and various chemical and biologic factors, define the subsurface environment. The present characters of rocks and fluids in the subsurface are the result of the influences of many changing environments which affected them during their geologic histories. The papers in this volume discuss important subsurface fluids, their origins, movements, and evolution in geologic environments.

M ost studies investigating the effects of removable partial dentures on abutment teeth have been performed in a laboratory setting. In vitro experiments simulate the periodontal ligaments, osseous structures, and residual ridges. Results obtained from in vitro researchI-* have given dentists insight into removable partial denture design, but still, some doubt exists as to how these prostheses function in clinical situations. Miihlemann”, 6 introduced the method of periodontometry to dental research. He accurately evaluated the mobility of teeth in the oral cavity by means of a dial gauge and force meter. The simplicity of his measuring instrument enabled him to obtain data from many patients. Fenner and co-workers’ measured tooth mobility changes during treatment with partial denture prostheses. Their results indicated that removable partial dentures produced significant tooth mobility changes. In this investigation, very little was done to modify the existing tooth contours. Rudd and O’Leary8 modified the existing research tools used by Miihlemann and performed a clinical study on partially edentulous patients. They reported that carefully planned removable guide plane prostheses were effective in stabilizing mobile teeth. Carlsson and associate9 found, in a longitudinal investigation of extension-base partial dentures, that the success of treatment was dependent more on biologic factors than on the design of the denture. No attempt was made in this study to measure tooth mobility. The following investigation was designed to study the effects of planned removable partial dentures on abutment tooth mobility in partially edentulous subjects with similar oral conditions.

The contemporary advances and opinions pertaining to materials and to physio logic and biologic factors of removable partial denture service have been discussed. Certain suggestions and recommendations are made in the hope of enhancing this dental health service as well as stimulating and encouraging dentists to render it.

THE following report is an analysis of 28 cancers of the thyroid seen in children between the ages of 4 and 18 years at the Memorial Hospital. They constitute 6.5 per cent of the 430 cancers of the thyroid seen at Memorial Hospital during the sixteen-year period between 1932 and 1948. The purposes of this report are threefold: 1. 1. To discuss the histologic types and metastasizing properties of cancers of the thyroid in the children that we have studied. 2. 2. To discuss possible etiologic factors as suggested from an analysis of environmental, familial, and other biologic factors recorded in the histories of these patients. 3. 3. To emphasize the importance of considering cancer of the thyroid in the differential diagnosis of tumors of the neck in children. HISTOLOGIC TYPES The 28 cases are catalogued according to the classification of thyroid carcinoma used at Memorial Hospital. This is a relatively simple classification which can be correlated with the clinical prognosis and the radioiodine concentrat...

To the Editor:— In connection with Dr. Novak's article "Two Important Biologic Factors in Fertility and Sterility" (The Journal, February 10), kindly allow me a remark or two. Births can be controlled in a "natural" or "biologic" way by complete abstinence (continence) or by observing the periods of sterility and fertility in women. Births can be controlled in an artificial way by making use of chemicals or mechanical devices and by coitus interruptus. In the one case births are avoided and in the other case births are prevented. This distinction is of great importance not only from an ethical point of view but also from a scientific point of view. Hence the expression "biologic contraception" to indicate natural or biologic birth control does not seem a very happy one. The word "contraception" should be used only in connection with artificial methods of preventing conception, because "contra" connotes prevention rather than

Much work has been done in recent years to clarify biochemical and neurologic factors in the vast and still confused field of "epileptic" disorders. The data observed, however valuable, have not yet been sufficient or adequately synthetized to explain convulsions. An important reason, no doubt, is the complexity of the factors involved and the fact that sufficient attempts have not been made to establish the interrelations with other biologic factors, and especially the setting in the whole psychobiologic unit—the personality. In studying an epileptic patient, one has to observe the type of integration which has been reached and the possible influence of part functions. This allows one to understand the influence not only of psychobiologic factors, but also of endocrinologic and other physiologic factors which are usually not analyzed but merely accepted (e.g., constipation and fatigue). Only in such a way will one be able to understand the factors which

ed by Francis H. Slack, M. D., andl Mr. James M. Strang. The Campaign Against Diphtheria in Belgian Luxemburg.-JIn the diagiiosis of (liphtheria time is lost by the necessity of cultural examination of the swab; direct examinationi being negative in so per cent of cases. Fatty material which is oll the swab p)revents anythlilng like a representative film of the bacteria present being made. The author proceeds to show how, by improved techi(lue one can obtain about 70 per cent of positives instead of the usual 20 per cent, by direct examiniation. On receipt of material the swab is inioculated on to serum medium. The tube of medium should contain at least 2 cC. of 'condensation water," in which the swab is soaked and then drawn over the surface of the medium in the usual way. The iluid in the soaked cottoni vool of the swab is then squeezed out on to a slide by means of flat forceps and spread into a film which is stained by Neisser. Lomrey found that fre(juenitly onie could j'udge of the probable result of the examinationi by the appearance of this fluid; if it proved to be milky in appearance, a positiv e result was almost invariably obtained and vice versa. The presence of a large saprophyte and a mould may give a little trouble owing to their bipolar granules which are stained by -N eisser. The presence of two large terminal graniules and a smaller cenitral one, equally spaced, shows that one has to deal with true diphtheria.-R. F. Lomrey, Ann. Inst. Past, 1919, 717. Abstr. in Jozur. AtSatc llcd., Feb., 1920. (D. G.) Biologic Principles in Public Health Work.-According to the author the un(lerlying ideas of almost any public health program are so seductively logical that it is only in recent times that any one has attempted in any systematic and strictly objective way to see what the program is actually accomplishing. The true test of the success of public health programs consists in analyzing what logically ought to happen and what actually is taking place. Intensive investigation of the fundamental biologic factors in the problems of public health are essential to further real progress toward their solution. As an illus4 ..3 tration the atitlor abstracts the results of a carefully conducted study oni the last influenza epidemic, notinig that the primary factor in causing Xvariations between differenit communities in respect of reaction to the infltienza epidemic was the organic fitness of these communities. Communities in some degree organically unsound as indicated by relatively high normal death rates from phthisis, organic heart diseases and nephritis were less able to meet successfully the attack of the epidemic than were those in which these organic diseases were not so prevalent.-Raymond Pearl, Jouir. A. Al. A., Feb. 7, 1920, 375. (D. G.) A Method of Standardizng Bacterial Suspensions.-The opacity of a bacterial suspension is measured by the length of the column of the suspension required to cause the disappearance of a wire loop. By a simple formula the measured cap)acity is translated ilnto terms of bac,eria pcr cc. and so made comparable with that of other suspensions of the same organism. An instrument for measuring the capacity of bacterial suspensioins is described in detail. Jour. E.rper. Mf,d., Jan. 1920, 105. Grouping of B. Influenza by Specific Agglutination.-Ten strains of B. inluenzw were tested for their specific and cro3s agglutinating powers. Nine of the strains studied had the typical cultural and staining qualities of B. influen-za, the tenth was less regular in its properties. The immunization of rabbits, preparation of antigen and agglutination tests was carried out in the usual manner, the tul)es being incubated for 16 hours at 553 before reading. The cross agglutination tests showed a marked grouping of related strains. Seven of the strains fell into two groups, group one having three strains; group two, four. The remaining strains did not cross-agglutinate, although they reacted to their own specific sera. This work demonstrates the possibility of the grouping of B. influenza?, organisms by immunological methods. -Small and Dickson, J. Iuf. Dis., 1920, 26, 230.

Second only to etiology, the most important phase of the practical study of tumors is the determination of the anatomic and biologic factors that facilitate or prevent metastases. The cause of cancer is as yet unsolved, but we know that the disease, regardless of its site of origin, ultimately spreads as metastatic growths throughout the body. The metastases may occur late or early, in nearby tissues or in more remote organs, and they are the important determining factor in cancer—usually bringing about the fatal result. Metastases represent cancer cells that have traveled to the point found and are growing as secondary tumors. Whether these detached tumor cells find their way by "spontaneous movements," by "permeation" or by "forcible dissemination," as has been stated by various writers, is of no particular importance. There are two general routes of tumor cell dissemination, lymphatic and blood. In most instances cancer metastases occur by

In 1910, Burrows1took up the study of cellular growth in vitro. Harrison2had studied the behavior of the isolated central nervous system, as well as other tissues of young frog embryos in hanging drops of fluid lymph obtained from the lymph sac of this animal. This lymph was not a good medium for cellular growth, thus Burrow's problem was that of obtaining a suitable one, so that cells of different types might be grown in vitro. Harrison was unable to obtain a growth of cells. He had obtained a growth of nerve fibers and a migration of the cells, but multiplication of the cells was not obtained. Burrows undertook to see if the cells could not be cultivated under some such similar conditions. The lymph which Harrison had used was not a good medium in that it could not be obtained readily from higher animals and it

The heredofamilial or endogenous diseases of the central nervous system are characterized by germ layer selectivity, system selectivity and segment selectivity (Schaffer). 1 The exogenous diseases of the brain and spinal cord, the etiology of which is unknown or which belong definitely to the group of infectious maladies, are localized in a characteristic way in the gray or white matter of the central nervous system. Both the gray and the white substance of either the brain or the spinal cord may be selectively the seat of pathologic alterations. Undoubtedly, local anatomic, physiologic and biologic factors play an important part in such selectivity. The nature of these local physiologic and biologic properties of the brain or the spinal cord is unknown. In regard to anatomic structure, it is known that the gray matter is more richly supplied with capillaries than the white substance, and this may result in physicochemical differences. In

The early enthusiasm that attended the discovery of the x-rays gave rise to their employment by methods that bore no regard to inherent physical and biologic factors associated with this form of energy. This disregard of these biologic factors led to many unfortunate reactions and sequelae both on the person of the x-ray operator himself and on the patient. Marcuse in 1896, according to Ewing,1made the first formal report of this condition, and Kienbock, cited by Ewing, in 1900 described in detail this x-ray dermatitis. Among the biologic reactions early recognized was that the x-rays caused epilation. It was found that this agent, when properly employed and applied only within certain fixed limits established by physical and biologic measurements, produced this epilatory result without destructive effect on the tissues to which x-rays are administered. The early advocates of x-rays suggested their use as a panacea for many skin

There are two distinct main aspects to the consideration of subacute bacterial endocarditis: (1) the mode of infection of the cardiac valves and (2) the factors involved in the continuance of the growth on the valve. The second aspect was the subject of the present investigation. We felt that it might prove to be of practical value to discover why infection due to a relatively nonvirulent organism persists on the cardiac valves. To this end the behavior of Streptococcus viridans was noted in various types of serum and whole blood, and the fate of the bacterium was investigated when placed in the blood stream, on a cardiac valve and in certain other tissues of the normal living dog. Horder,1Schottmuller2and Libman and Celler3first observed the morphologic characteristics of Str. viridans and noted its relative nonvirulence. Since their observations innumerable studies have been made of the