Herbert L. Ratcliffe

Changing frequency of arteriosclerosis in mammals and birds at the Philadelphia Zoological Garden: review of autopsy records.

From 1901 through 1932 arteriosclerosis was found in less than 3 per cent of autopsies on mammals and birds at the Philadelphia Zoological Garden, but thereafter its frequency has increased to about 20 per cent. This study has attempted to identify factors that may be associated with this change in frequency.

Morphology and Life-cycle of an Amoeba Producing Amoebiasis in Reptiles

The morphology and life cycle of an amoeba producing amoebiasis in reptiles is described. The organism is assigned to the species Entamoeba invadens Rodham 1934, because of the pathogenicity of that species. Material for the study was derived from 30 individuals of 7 species of reptiles, either dying of spontaneous amoebiasis or experimentally infected. (Material from 3 additional species of reptiles dying of amoebiasis was not used in this study.) With the exception of a few minor morphological differences, E. invadens was found to be strikingly similar to E. histolytica in morphology of trophic and cystic stages, and in the processes of encystation, excystation, and metacystic development. Metacystic development was studied in stained preparations made from the intestines of snakes 1–24 hours after the inoculation by mouth of mature cysts. Excystation usually takes place in the jejunum and ileum, a single quadrinucleate amoeba hatching from each cyst. Each quadrinucleate metacystic amoeba ultimately forms 8 amoebulae as a result of one division of each cystic nucleus, cytoplasmic division, and parcelling out of the cystic ( N ) and daughter ( n ) nuclei. Nineteen of the 24 possible combinations of N and n nuclei were observed. The culture phenomena of multiple fission without encystment is suggested, and cannibalism of cysts by the trophozoites is described.

Changes in the Character and Location of Arterial Lesions in Mammals and Birds in the Philadelphia Zoological Garden

Improved nutrition for mammals and birds at the Philadelphia Zoological Garden has been followed by continued increases in the frequency of arteriosclerosis and by changes in the character and location of the lesions. During the first decade after diets were improved the large atheromata of the proximal aorta and brachiocephalic arteries of birds were replaced by smaller, more compact lesions, usually of the abdominal aorta. At the same time many species of mammals developed atheromata of the aorta, whereas earlier these lesions had been found chiefly in baboons and monkeys (Cercopithecidae). During the second decade of adequate nutrition, and especially since 1950, arteriosclerosis of the coronary arteries has become relatively common in both mammals and birds. Usually this lesion has developed in the distal, intramural segments of the coronary arteries, as intimal thickening and occlusion. Most frequently it has been associated with myocardial fibrosis, but it also has led to myocardial infarction and sudden death in both mammals and birds. Present evidence suggests that this lesion reflects a response of adequately nourished animals to population densities.

THE SIGNIFICANCE OF NATURALLY OCCURRING CORONARY AND CEREBRAL ARTERIAL DISEASE IN ANIMALS

Attempts to establish the possilde fatal consequences of chronic arterial disease in nonhuman species are hainpered by two circumstances. Firstly, when death is sudden and unexpected the suhject is either disposed of without being necropsied or, if necropsied, only perfunctory attention is given ordinarily to the cardiovascular system. Secondly, animals are usually slaughtered or die of infectious, parasitic, traumatic, or nutritional disease before they become aged and before progressive vascular disease has run its course. The studies briefly reviewed here have resulted from efforts to obtain information regarding the role of arterial disease in animals that have died suddenly and in aged intlivitlual\. For oyer 60 years, all animals dying. suddenly or otherwise, in the Philatlelphia Zoological Garden have been necropsied, with special attention 1)eing given to the cardiovascular system. These records provide data on t!ie association of arterial disease and sudden cleath.1-2 The natural history and epitlemiology of cardiovascular disease in dogs presented to the clinic of the Scliool of Veterinary Medicine. University of Pennsylvania. have heen studied for about 20 years, giving opportunity to observe the sequelae of chronic arterial disease in aging individu a l ~ . ~ . ~ Approximately 1 5.000 dogs have heen examined for clinical evidence of cardiovascular disease : of these. m i i e 1,200 have 1)een examined postmortem. Additionally, a series of .50 agetl pigs. eight to 14 years old. and 100 pigs of younger age g r o q s . incliitliiig 40 kept under experimental conditions, have been obtained for postmortem studies, especially of the cartliovascular systeni.5*6 These records providc data on arterial changes and their sequelae in aged individuals of two doniestic species.

Myocardial Infarction: A Response to Social Interaction among Chickens

A study of male and female chickens caged alone, in male-female pairs, in groups of four males and in heterosexual groups of 6, 12, and 24, with a proportion of two males to one female, suggests that coronary arterial disease with myocardial infarction may be a response to social interaction, especially interaction that relates to sexual behavior. Myocardial infarcts were limited to males of heterosexual pairs and groups and to females of groups that contained 24 chickens. The lesion was found in males that died at 16 to 44 weeks of age, and in females at 32 to 43 weeks.

Coronary Arterial Lesions in Chickens Origin and Rates of Development in Relation to Sex and Social Factors

Single-comb, Hy-line white leghorns were hatched in one lot, brooded in one flock through 7 weeks, then assigned randomly to cages in one large room with 15 hours of light per day. The birds were studied in the following situations: a) separately caged cocks and hens, b) paired cocks and hens, and c) 3 cock-3 hen groups and 6 cock-6 hen groups. Basic space allowance was 2 square ft per bird which was increased to 8 square ft for some of the larger groups. Commercial rations and water were supplied ad libitum. Stenosing lesions of the intramural coronary arteries began development in cocks and hens before age 7 weeks (10 to 12 weeks before sexual maturity) and progressed with age. Progress, as measured by heart scores, was not influenced by space allowance but was related to social situation. The rate for separately caged cocks was significantly higher than for other birds. Cocks of the larger groups and cocks of the pairs were next in order, while heart scores for cocks of the smaller groups were third but not significantly higher than for grouped hens. Heart scores of grouped hens sometimes exceeded heart scores for cocks of corresponding groups. High mean heart scores for grouped cocks correlated with high mean heart scores for hens of their groups, and low heart scores for grouped cocks with low scores for hens of their groups.

Editorial: Environmental Factors and Coronary Disease

E NVIRONMENT may be defined as the interaction of external and internal forces that encompass the individual, the colony, or the species. The more obvious of these forces are climate, food, and intraspecific relationships. Thus attempts to relate environmental factors to the etiology of cardiac coronary disease are confronted with highly complex mechanisms. For example, living standards for large segments of the population of a number of countries have improved appreciably as one result of continued industrial growth. These more abundant economies are reflected in an increased food intake, especially animal protein and fat.1-3 Industrial growth also has been accompanied in recent decades by rapid urbanization.4 Accordingly, increases in population density, as well as in social and economic competition, must be recognized as other environmental changes that accompany economic growth.k9 Apparently then the exponential increase in the frequency of coronary disease of recent decades cannot be attributed wholly to changes in dietary habits. It may be related equally well to changes in intraspecific rela-

INFECTIOUS DISEASES OF LABORATORY ANIMALS

Whatever the field of investigation, or the immediate problem to be studied, one may say that the experimental biologist more often than not has hope rather than assurance that his animal subjects are healthy. When one is concerned only with short-term studies, perhaps the source and care of experimental animals need not be considered so completely. Yet, certainly, any experiment demands that variables be reduced as much as is possible, which, in turn, demands standardized animals maintained under standardized conditions. This goal may not be completely attainable, animals being what they are. One obstacle is the considerable number of infectious agents to which laboratory animals are susceptible. Under natural conditions, the species from which laboratory animals are derived are subject to many of the same infections that occur in captivity, yet they survive and multiply. One wonders, a t times, whether or not efforts have hrrn misdirected. Possibly, colonies of laboratory animals should be fully exposed to infections, until, by selection, highly resistant strains are obtained. Certainly, present-day efforts to exclude infections develop highly susceptible races. Nevertheless, the chief concern of this review will be the more important infectious disease of the following species of animals: rats, mice, guinea pigs, rabbits, dogs, cats, monkeys, and canaries. To a large extent, housing and care of colonies of these animals are modified by the necessity of guarding against infections. Hence, these phases of the topic will be considered only as they apply to control of contagious disease. Location of animal-rooms and their construction, the size and arrangement of cages, the temperature a t which quarters are kept, and hygienic considerations have varied widely as different laboratories have sought to meet the nerds of one or another species. Certainly, considerable variation is possible without neglecting essentials. This much is certain, animal-rooms should be proof against wild mice and rats, and against insects. They should be adequately lighted, ventilated and heated. Walls and floors should withstand thorough washing, with satisfactory drains to allow rapid drying. Tables, cage-