Part 3

It would seem therefore that it is not unfair to use material gathered from animals under somewhat unnatural conditions as representing the reaction of the zoological orders to pathogenic agencies. Such conclusions must however be made very guardedly, for it is probable that not over ten per cent. of the total number of mammalian and avian species are to be observed in captivity. Because of the number of orders and the great variety of genera included in the present study it is probable nevertheless that the lesions are fairly representative of the whole animal kingdom.

However, the numbers and percentages given should be read to indicate the probabilities and should not be interpreted as implying the mortality relationships since different varieties have differing powers of resistance to the same pathological state. The margin of safety in any given group for one or several different disease entities cannot at present be stated with any degree of precision but this factor is doubtless very great. The work of physiologists suggests that there is a reserve power in the human lung sufficient to sustain life until five- sixths of the functionating organ is useless, and I shall quote a case of an opossum wherein only one-tenth of the respirable surface seemed to have remained; we have repeatedly seen both lungs of a monkey apparently entirely solid. Such physical vital incompatibilities might be exemplified by many other cases, but when one reviews the physiological margin of safety, inexplicable and contradictory instances are equally numerous. I have seen a male deer run a doe against the fence and butt her, without result, whereas in an apparently similar occurrence the animal would be dead in a short time. Numerous instances of slight enteritis of a short stretch of duodenum or ileum have killed, with almost nothing to be found microscopically, and on many occasions we have been chagrined in being unable to discover the cause of death. The capacity of self-healing is a variable one, but seems in direct proportion to the quietness and seclusion possible for the animal and inversely to the chance of bacterial infection.

The effect of captivity has been the subject of much speculation. For the preservation of health it would seem that animals require periods of rest and activity, thorough elimination, possibly a moderate exercise of their procreative functions, but most of all, appropriate food obtained by the physical effort we term chase. All but the very last condition is supplied in a measure in well managed collections. The degenerating effect of the absence of chase must be admitted. An interesting and suggestive example of this was noted by Mr. Jones at the London Zoological Gardens. He observed the skull of a lion that had been in captivity thirteen years, in which the canine area of the face and the part of the skull acting as the insertion for the seizing and holding muscles had undergone atrophy while the chewing muscles with their bony bases had remained normal. Numerous examples of disease atrophy are on record and those of a physical nature must have counterparts in the realm of physiology. The size to which an animal will attain cannot be estimated by the examples seen in menageries. Judging by the accounts of collectors and hunters and upon the more reliable of the moving picture displays of wild animals in their native haunts, it would seem probable that under normal conditions of habitat the average size of wild beasts is considerably in excess of that in park specimens.

The effect of captivity may also be felt in the direction of reduced resistance to infectious diseases. Brooks, of the New York Park, expresses the view that captivity increases susceptibility to bacteria and causes parenchymatous degenerations. In the latter direction it is interesting to learn that Seligman of London claims to have seen sudden deaths in wading and struthious birds from myocardial disease, without valvular or other lesions, for which he holds the enervating effects of captivity responsible. It is well recognized that a species may be unusually susceptible to a disease that it has not encountered in its phylogenic development. Man illustrates this peculiarity very clearly. Europeans were found exceedingly susceptible to sleeping sickness when they went first to the part of Africa inhabited by the tsetse fly, and the American Indians died in hordes when they met the tubercle bacillus for the first time. Judging by the ravages of tuberculosis in captive monkeys a similar susceptibility probably explains the matter for there are no entirely satisfactory records of this disease among them in the wild state.

In so far as general susceptibility to infection is concerned, it may be in part due to one of the artificial conditions of captivity, that of inbreeding. This influence is undoubtedly very great, both by chance in families, and by intention on the part of dealers as well as the mating which occurs in menageries. However, it is not known how far inbreeding may go in the wild state so that one must be very careful about drawing conclusions in this particular. Several years ago, at the time we reported the neoplasms found at the Garden, discussion arose as to the effect of inbreeding, and thereafter some observations were made in this direction. With the exception of the hyperplasias of the thyroid, not certainly of neoplastic nature, in a much mixed-up family of wolves, we could find no evidence that inbreeding was responsible for tumors. Plimmer and Murray of London, seem to imply that some of their inbred animals are likely to have tumors; reference to this matter will be made later in this book. In so far as diseases of the organic systems are concerning those of the bones seem to be the only ones in which inbreeding is significant.

The individual resistance will be reduced of course by the unsanitary surroundings incident to trapping, shipping and storage, but this need not affect the figures or pathological tendencies of classes or orders.

The effect of captivity is felt in another way. A very large percentage of wild life perishes during the first weeks or months after its capture, and in gardens the heaviest mortality occurs among the recent arrivals. The London Garden figures that from thirty-three per cent. to fifty per cent. of their total mortality is in animals that have not been in the garden six months and that die because they are not yet accustomed to their new surroundings. It seems to us, both from an academic and a practical standpoint, that this is a long time and should afford ample opportunity for the garden to study the specimen and for the specimen to become acclimated. These early deaths are perhaps to be ascribed in large part to failure of acclimatization but many are doubtless the result of infection acquired in the wild, in transit while in the hold of vessels, at quarantine, or in trains, or at the establishments of dealers. We have seen a few deaths which have followed behavior that might be likened to homesickness. Perhaps the age at arrival has an influence upon the morbidity and mortality of wild animals, for it is easily conceivable that the young and the very old might adapt themselves to new surroundings with much less readiness than the sturdy middle-aged adult. The age of animals upon arrival is very rarely known, and can only be recorded as “young,” “fully developed,” and “old.” This will have an effect upon statistics and when possible is noted in the text, but this is not practicable to the extent we desire. The meaning of “young,” “adult,” and “old” is not the same throughout the animal orders nor even within orders.

Mitchell[3] has attempted to gain concrete ideas of the expectancy of life among animals by analyzing the records of the London Gardens. This gentleman bases his figures upon known ages and the length of time in captivity, from a combination of which data the specific viability and the potential longevity may be estimated. Such results, he admits, can only be approximate and they show within classes and orders, a decided lack of uniformity. The terms “specific” and “potential” longevity, coined by Sir Ray Lankester, apply, for the first, to the average length of life as it is affected by external conditions and those incident to procreation, while, if an animal be under ideal conditions it will attain the potential longevity which is longer than the former. These considerations have a biological and economic importance, while a knowledge of the pathology shown by the various groups may help to explain these durations of life. Contrariwise figures of the expected longevity may assist us in evaluating youth and senility in the causes of death but can hardly affect the comparative nature of the lesion.

A résumé of Mitchell’s studies indicates that the higher apes have a potential longevity and a hardihood much less than man but still upwards of thirty years. As one investigates lower in monkeys, life periods become shorter, while in the next order, Lemures, the length of life rises. Carnivora have a reasonably good vitality, their potential periods varying from ten years in the foxes to thirty-three years in bears. Insect eating animals are short lived, three years being a maximum. The Bat family shows great variations, the greatest life being not over seventeen years. The Rodentia have long lives compared to their sizes—twenty years in porcupines, fifteen years in squirrels, thirteen in marmots, nine in agoutis and capybaras, and three in dormice (which is also about the maximum for the rat). Hyraces live four years on the average. Proboscidea, although reputed to live to great age, probably rarely live a half century and may be said to have an expectancy of twenty to thirty years. Perissodactyla (horses, tapirs and rhinoceroses) while they may live half a century, have an average life of between fifteen and thirty years. The closely related Artiodactyla fall into two groups, a first comprising antelopes, sheep, goats and deer which rarely exceed seventeen years, and a second consisting of cattle, camels and giraffes, which vary in expectancy from eighteen to thirty years. The smaller members of the Ungulata have in relation to size a relatively greater viability, the ruminants, however, having on the whole a low viability. Marsupials vary from a maximum of seven years in the opossum to eighteen in the wombats, but none of this group has a good viability. The Aves as a class or if compared according to dietary requirements, have longer potential ages and better viability than mammals. Passerine birds average twenty years and many live to sixty, while the Picariæ approach the former figure but do not have such good viability. Psittaci and Striges may live a half century but the resistance of the latter is much reduced by any unfavorable surroundings. The raptatory birds live fifty years, but their viability is variable. Herodiones have a maximum expectancy of thirty years and good resistance, while their relatives, Steganopodes, may live fifty years, and Odontoglossæ have a good viability, up to twenty years. Anserine birds may live to be fifty, and, unless conditions are quite unfavorable, have a good resistance. Columbæ may under good conditions live to be fifty. Gallinaceous birds may only be expected to survive twenty years, a figure also given for Fulicariæ. Alectorides may live up to fifty years. Limicolæ, though they do not thrive in captivity, may live thirty years. Impennes live poorly under artificial conditions, the greatest record being twelve years, a figure also holding for Crypturi. Struthiones, if the conditions be right, may live fifty years.

Because of the variable specific longevities, it is frequently difficult to decide when an animal is senile. Man is said to be as old as his arteries, and his span of life nowadays is in the neighborhood of half a century. Parrots exhibit lesions of the vascular system comparable to the arteriocapillary fibrosis of human beings, and their expected longevity is about the same or a little greater. From a study of our cases of this lesion in parrots it can be said to appear quite early in life and not to lead to organic disease as it is alleged to do in man. It is, however, interesting to note that in those animals which are supposed to have the longest specific lives—elephants, snakes, anserine and raptatory birds, parrots—there is relatively low mortality and fewer infectious diseases are encountered. The last part of this statement should be qualified by stating that anserine birds and parrots are quite susceptible to mycoses, in all probability from musty food, which raises their death rate, but as this is accidental and artificial, it can be excluded from consideration.

In a rough way there is a direct relationship between the size of an animal and its longevity, but this is not close enough to be a reliable guide; whales and elephants live a long time, but so do snakes and parrots. Within orders this relation of size and expected longevity is more easily seen but is not absolute. I cannot state, according to my present studies, that there is an unqualified relationship between the size and expected longevity of an animal and its pathological lesions.

The immediate surroundings and the management of captive animals have a very direct and important bearing upon the mortality and perhaps upon the incidence of morbid processes but probably not upon the character of the latter. A full knowledge on the part of the personnel of a zoological society concerning the habits and habitat of every animal in their keeping is essential, to which must be added a group of interested keepers. In engaging the last, it should not be forgotten that certain men have “a way” with animals and that others cannot manage themselves.

The enormous literature at the disposal of the naturalists permits executive officers to formulate a plan of housing and feeding with fair accuracy for each kind of animal, but of course it is rarely possible to obtain in sufficient quantity the natural food (_e.g._, ants for anteaters). In so far as food is concerned it seems that with a few exceptions like the one just mentioned, the substitutions made at the zoological gardens are nearly satisfactory. The elements in which the captive diet is poor are the inorganic salts and vitamins since Dr. Corson-White, some of whose work is included in a later chapter, has shown that for those animals which our statistics indicate as most prone to have rickets and osteomalacia, the available phosphorus and calcium are low, and one vitamin was also below the desired quantity. In this regard, however, I am not at all convinced that diet alone will suffice to explain these degenerative osseous diseases; I shall take this up more fully later. Careful inspection of all food should be made and cleanliness (sifting of cereals, protection of meat from flies, etc.), is indispensable. The mortality among our carnivora has materially decreased since the horse meat after butchering was placed in covered galvanized iron pans. There are many problems of feeding, too numerous to be covered in a survey of this sort, which must be solved, and it is a credit to superintendents that this they have studied carefully.

There are two problems in the management of animals upon which much difference of opinion exists, namely the heating of houses and the material of which cages are made. It seems to be the practice in many gardens to keep animals very warm. Dr. Chalmers Mitchell states unqualifiedly that adult animals do not have to be kept warm, and that even an equable temperature is not demanded, variations in temperature having a distinctly stimulating effect. However he maintains that they should be kept dry and must be supplied with a shelter. This is in accord with the experience at the Philadelphia Garden, since for many years we have allowed access to the open air all winter to every animal that could stand it. A large group of macaques has now lived entirely in an open “band stand” cage for nine years with a lower mortality than in the rest of the monkey collection, which is permitted to go indoors some of the time. Occasionally one in poor health is frozen to death, and healthy ones may lose fingers, toes, or a part of the tail, but the general condition is so much improved that they present an attractive exhibit to visitors. Unless a storm be of great severity, wild animals are usually indifferent to it although they may seek their shelter. Snow apparently is no source of fear to them, and many enjoy playing in it. The general principles of the enclosure should be proper lighting, free access of air, dryness and shelter in time of storm, the last so arranged that the sleeping place is well protected. Appropriate arrangements should be made for nocturnal animals, regardless of their visibility to visitors, if their preservation is of importance.

The hygiene of communicable disease has influenced everyone to use concrete and metal for cages. These substances are without doubt most simply kept clean, but they are heat-conducting and remain cold or damp longer than wood or the ground. It may be claimed that the latter two cannot be disinfected so well, but this need not militate against their use. Wood can be disinfected by sunlight or by mechanical cleaning plus disinfectants, by a blast lamp and by paint. The ground will disinfect itself if allowed to lie fallow for a time, or it may be turned over after sprinkling with lime. It is fair to note that the New York Zoological Garden reduced their mortality, especially from verminous pneumonia, by changing some deer herds to concrete paved enclosures; if that were the only change made the result would be very significant, but it should not be forgotten that another clean ground range might have served as well to a herd from which the infected ones had died. My own observations with guinea-pigs, rabbits, mice and dogs lead me to believe that they thrive and breed better on wooden floors than on metal or stone.

I have tried to work out figures to show that more animals die when housed in enclosures of stone and metal than when upon the earth or on wood, but the attempt has been unsuccessful chiefly because of the presence of epidemics and parasites, principally among the birds. The attempt was further embarrassed because some members of an order are housed on both floorings. However, there was no great advantage for the metal and concrete floors even after the epidemic had been discounted. This Garden does not have a great number of pneumonias, a disease said to be favored by dampness and cold, but those that occur are chiefly among the small mammals, on wooden floors and in the large bird house in cages of concrete and metal. However, the construction of both these houses permits the visitors to approach very close to the cage, a factor that doubtless explains the disproportionate incidence of inflammation of the lungs. In so far as outdoor fowl and ungulate ranges are concerned, they should be changed frequently under the best conditions since occasionally one will find groups doing badly until moved. Moreover the ground becomes contaminated with parasites such as esophagostomum and heterakis, infestation with which while not very serious in itself, may lead to fatal infection with bacteria.

The effect of animal parasites upon the morbidity and mortality of wild beasts and birds in captivity is by no means clear, and Doctor Weidman and I are inclined to be sceptical, with certain reservations of course, of their great importance in the death rate. Doctor Weidman has kindly agreed to contribute a chapter upon the general distribution of protozoal and metazoal parasites with a summary of their probable pathogenic importance.

The groups known to have a decided pathological power might be divided into the toxic, the tumor formers and the mechanically obstructive; certain parasites have properties placing them in two of these classes. The first group comprises the hemosporidia and hemogregarines, the uncinaria and some of the cestodes, forms which produce hemolysis and hemorrhages with varying grades of anemia. The importance of this group is shown chiefly among the Aves, in which high grades of anemia are occasionally met from malarial infections, but cats and dogs or even herbivores also frequently suffer from hookworm. The tumor-producers are chiefly echinococcus worms, the cysts of which may grow large enough to occupy nearly the entire abdomen. A certain grade of anemia and general ill health accompany this hydatid disease, partly the result of a toxin and partly by damage to important viscera. Those parasites which obstruct mechanically do so by their own bulk or by an accompanying inflammation, incited by them as foreign bodies or by bacteria which have gained entrance at the irritated point. This is exemplified by the enormous collection of nematodes sometimes found in reptiles (a pailful was removed from a python) and by the tightly coiled or tangled thread and tape worms frequently found in birds. The effect of swelling by the mucous membrane under the influence of worms is illustrated by the infestation of the proventricle in parrots. Here spiroptera penetrate into and under the glandular layer which swells and pours out mucus, the total mass of nematodes, mucus and tissue obstructing the passage.

Very many animals show parasitic infestation at postmortem, but the percentage in which they can be said to be principal causes of death is quite small, while that in which they play a rôle as activator of the terminal condition is also small but indeterminate. The latter group comprise, together with the anemias mentioned above, certain forms of pneumonia, of hepatic and vascular lesions. Inflammations of the lungs from ascaris and paragonimus are fairly well known; fortunately we have been troubled less with this than have most gardens, possibly because we do not have such large herds of herbivora susceptible to it. Hepatic diseases from flukes, from coccidia and from amœbæ we have always with us in small numbers, but they are unimportant excepting enterohepatitis, a condition which appears in nearly all orders. This last disease, be it purely amœbic as in dysentery of man and monkeys, or like blackhead of turkeys and chickens or in the forms of quail disease, arrests the attention at once and evokes a desire to explain the association of large intestines and liver. Parasitic vascular lesions are relatively unimportant.