Part 51

Evidences with which to trace transmissions are much clearer in the birds than in the mammals with the exception of monkeys and some ungulates. Of course cases are perhaps too few in the carnivores and rodents to permit correct deductions but it is very rare that more than one case occurs in the same enclosure containing groups of these varieties. Nor do animals in adjoining cages seem to “catch” the infection. This observation does not suggest that any relaxation of hygiene need be allowed but probably it implies that not many bacilli are excreted by these animals; they cough very rarely. Groups of ungulates (bison and deer) are often known to be infected but just how it has arisen is seldom clear. Transmission from monkey to monkey has been observed so frequently that it cannot be doubted, nor will anyone wonder at it if reflection is given to the close personal contact of these animals during their natural behavior. They huddle, pluck lice from one another, take food from the mouth of another, bite and perform many other actions greatly facilitating the transfer of any virus. Bacilli may also be disseminated by coughing, drooling and with the fecal discharges, for which latter there seems ample opportunity since a notable percentage of cases have intestinal lesions. Monkeys do not seem to raise sputum and expectorate it but they do eject saliva from their lips.

Contraction of the disease from infected cages is believed to have occurred at least once in our experience but the lesson of complete sanitary cleaning of the enclosure learned from that happening, seems to have enabled us to forestall its repetition.

THE TUBERCULIN TEST.

Tuberculosis presents the greatest single problem among the specific infectious diseases which the director of a menagerie must attempt to solve. Even though one may possess a knowledge of its zoological distribution, clinical characters and pathological effects, these are insufficient criteria for its detection at a stage when the animal might be saved by treatment or, what is most important, removed from its companions that they might be protected. To this end there remains but a single procedure for the discovery of the existence of tuberculosis—the use of tuberculin in one of its forms by one of its methods of application. The use of this test in veterinary medicine needs no commentary, having made its place in clinical and hygienic practice for a quarter century or more. Armed with the knowledge of the satisfactory use of the toxins of tubercle bacillus in cows, Dr. Penrose, Dr. C. Y. White, Dr. A. E. Brown and Dr. Leonard Pearson began in 1901 a series of experiments with old tuberculin of Koch which have led to the development of a technique for its use in the detection of infected monkeys. These interesting and instructive animals, being known as highly susceptible since most of the collection died of the disease in those days, and being handled with reasonable ease by experienced men, were investigated as the most important specimens upon which to perfect the method. Other varieties have been studied since and I shall refer to them individually. The greatest amount of work and the most conspicuous success attended the observations upon monkeys and the results of this study are now in daily use in this Garden.

The work, conclusions and results, originated by Doctor Penrose, Doctor White, and Doctor Brown can be described as one of the most completely satisfactory series of observations in scientific medicine. Applying the principle that a tuberculous animal reacts to the injection of tuberculin by a temperature rise, the normal temperature curve of the monkey was studied, that of the tuberculous monkey determined by killing many specimens. This enabled them to state which animal was infected, which was not and to place on exhibition only healthy specimens. Added to this, strict hygienic principles in the housing and handling of the animals have resulted in the elimination of the disease from our exhibition house. Occasionally a case may develop, perhaps from feeding by visitors, but the matter is no longer a problem. I know of no more complete and satisfactory experiment and its practical application than this work, which is condensed in the succeeding paragraphs.[101]

THE TEMPERATURE OF MONKEYS.

The success of the tuberculin test in the lower animals as in man depends chiefly upon the alterations in temperature following the injection of the toxin. It is generally admitted to-day that a healthy animal’s temperature will not be affected by the introduction of this material. There are in addition changes in the pulse and respiration rate and in the physical signs but these are detected with difficulty and are much less definite than thermometric records. The first essential was therefore a thorough familiarity with the normal temperature of the monkey, a requirement which met with considerable difficulty from the beginning since the earliest observations revealed puzzling irregularities. This necessitated the establishment of certain regulations of technique which, after the preliminary tests, have been found satisfactory enough to continue until the present day. All monkeys are received in the quarantine rooms of the laboratory where they are observed by the officials of the Garden and of the laboratory and there they remain in separate cages until passed, as free from tuberculosis, to the exhibition house.

The handling of monkeys for the purpose of taking temperatures is a matter of no small importance since excitement will quite definitely increase the registration. We have been fortunate enough to have in charge of this work since its inception the same man, Keeper McCrosson, who is thoroughly experienced in the care of these beasts and who can catch and hold them with a minimum of disturbance. To him and to the interested laboratory helpers much credit is due. Small specimens like capucins and spider monkeys are caught with the gloved hand or with the protection of a piece of heavy cloth. Larger specimens may be caught in a net while strong monkeys are fitted with a collar and chain by which they are pulled into the corner of the cage and held, while the door is opened to permit a helper to catch the feet and arms. Two experienced men can take the temperature of any monkey that can be handled at all safely. The knowledge of how to do such work reduces the excitement of the animal and renders more accurate the observation of its temperature. During the period of temperature-taking food is given in small quantities and only after the record is made.

Temperatures are taken in all animals by rectum,[102] the thermometer, a separate instrument but always the same for each animal, well greased with plain vaseline, being passed along the anterior rectal wall and allowed to register for twice its indicated speed. During the preliminary work, special instruments of officially standardized accuracy were obtained by Doctor Brown but once the normals were obtained, ordinary good thermometers registering from 94°F. to 108°F. have been employed. If the record vary very much from the expected, such as the figures obtained at the same time on the preceding day, or if the rectum be crowded with feces, the instrument is shaken down and reintroduced. In order to facilitate timing of exposures we use sand glasses of three minute run.

After some experimentation by taking records at various times of day it was found that monkeys as a group do not have a uniform temperature during twenty-four hours but register a higher figure during daylight than during darkness. This is probably due, as I shall discuss, to the period of activity, not to the time of day. Figures obtained at various hours indicated that the highest and lowest temperature would be obtained if records were made at four-hour intervals at three, seven and eleven o’clock AM. and PM. To give the normal temperature of a monkey, the kind and the time of day are necessary adjuncts. Reference to forty- eight hour charts which are used for the illustration of normal records, and for contrast with tuberculin reactions later, will convey to the reader a better idea of the normal daily rhythm of the simian heat regulating system than would verbal description.

NOTE.—In the temperature charts degrees indicated by circles and connected by dashes are from records made after diagnostic tests by injecting tuberculin.

The anthropoid apes (Curves A and B) have on the whole a mean temperature nearer the human being than do the lower monkeys, but they too present daily variables far greater than man. The high point of their curve, at three PM., is in the neighborhood of 100°F. the lower point around 97.5°F. From these charts and other records it can be said that while the higher apes have a daily temperature curve with its high point at three PM. and its low point at three AM., there is in them not by any means the regularity of curve to be found in Cercopithecidæ and Cebidæ. Our records of temperatures in the Hylobates (_Gibbons_) are not extensive enough to quote but what we have approach those of the lower monkeys.

Graphic curves of the normal temperatures of the various genera of Cercopithecidæ and Cebidæ present striking similarities in the regularity with which the daily rhythm is performed. In the seven genera of which we have accurate records the normal high points fall between 102°–103°F. and the low points between 99°–100°F. while the curve of the four-hourly steps is closely comparable. The curves D to J are composites from charts of animals that have been tested with tuberculin, which thereafter died or were killed and found free from tuberculosis. Not every individual chart that may come to hand necessarily follows the exact course detailed in these illustrative curves but these latter offer a guide as to what is to be expected of the different varieties. They show unequivocally the V-shaped curve of the temperature of the monkey during twenty-four hours.

The Callitrichidæ or Hapalidæ have failed to show tuberculosis in our Garden and little has been done upon them. As a matter of record there is reproduced the only satisfactory chart at hand (K) taken very early in the researches. It shows a similarity to those of the higher monkeys; because of its very high afternoon record the animal was killed; no tuberculosis was found.

The Lemures, being close to the Primates zoologically and presenting a high incidence of tuberculosis, were included in this study. Observations upon their normal temperature were hampered more than upon that of monkeys and even to-day we cannot feel the same confidence in the records. Irregularity is most marked and they seem easily disturbed by handling. Chart C shows a composite temperature for forty-eight hours of twenty-two proven non-tuberculous Lemures. The tendency for the “night drop” is certainly existent but with much less definiteness than in the Primates.

CONDITIONS WHICH MODIFY THE TEMPERATURE.

Observations by A. E. Brown[103] and by Simpson and Galbraith[104] would seem to indicate that the diurnal variation in monkeys is due to periodicity of activity. Doctor Brown found that the temperature of a night monkey is reversed, that it is higher during the dark than the daylight hours. See chart of Potto (_Perodictus potto_) chart L. The Scotch observers report that if the activity of day monkeys were reversed, daytime being made artificially dark and activity forced during the night, the temperature curves were likewise reversed.

Perhaps the most important discoveries of these investigators concerned the influence of excitement upon the temperature records. These observers indicate definitely that the greater the physical activity and nervous excitement the higher the thermometric record. We have noted that the substitution of a strange keeper who may not be gentle and tactful with the monkeys can serve to raise the temperature above the records obtained by an experienced man with whose methods the animals are familiar.

A knowledge of these facts dictates at least two important precautions on our part—our specimens must be kept under identic conditions peculiar to their kind, and surroundings must be established offering comfort with a minimum of annoyance in transfer and handling. To this end all specimens upon receipt are put into separate cages suitable to their size and allowed to become accustomed to their surroundings for several days before attempt at temperature-taking is made. Mention has already been made of the experience and interest of the principal keeper; the regularity of records is an attest to his work. Daily three o’clock afternoon temperatures are taken first to accustom the animal to the matter, before test records or tuberculin injections are made.

The existence of pathological states undoubtedly affects normal temperature curves and tuberculin reactions. Gastroenteritis has the effect of increasing the whole level and of making irregular the midday and afternoon records. Respiratory tract disease cannot be said to have a very definite effect; its most frequent influence seems to be to drive the night records lower so that there is a long fall between seven and eleven PM. and a long rise between seven and eleven AM.

THE TEST.

The preliminary rest of the new arrivals having passed daily three o’clock afternoon temperatures are taken until an even level is obtained; this requires usually four days but in very nervous specimens it may be much longer. The afternoon temperature course provides not only a means of teaching the monkey what is coming but supplies us with a high point record for comparison. When a new variety is received, a full normal twenty-four hour record is usually made. This preparatory routine being fulfilled, the animal is injected under the skin of the thigh or flank with freshly diluted mixed bovine and human tuberculin.

THE DOSAGE.

Early trials with this substance revealed the fact that a dosage based upon the weight in comparison to man failed to elicit a definite response whereas if based upon relative weight of cow was too large. The finally determined quantity was arrived at, as was the case in early human and bovine work, by experiment and trial and was as follows: A monkey of five to ten pounds (2.3 to 4.5 kilos) received an initial dose of 1. milligram and for each additional five pounds (2.3 kilos) 0.5 mg.; this is 0.2 to 0.4 mg. per kilo. The amount given to man varies from 2. to 5. mg.; if the body weigh 60 kilos this is 0.03 to 0.08 mg. per kilo. Cows are given usually in this country 400 mg. or, for a cow of 250 kilos, 1.6 mg. per kilo. In the early work, doses comparable to the figure for man failed, whereas at least two animals died very quickly after 1.+ mg. per kilo; 5. mg. was the original high dose. While the death of a monkey after a large dose was of no moment and was perhaps desirable, it would only be the heavily diseased specimens and this would give no criterion upon which to judge the appropriate dose for all. Experience seems to warrant us in continuing with our present figures since all tuberculous monkeys have reacted to it. Subsequent cases for retest are increased from 50 to 100 per cent. depending upon the size of the monkey, the very robust and vigorous ones receiving an increase represented by the higher figure. One monkey injected eight times has risen from 1. to 24. mg. with constantly a negative response over a period of nine years.

Doses for Lemures are relatively higher, averaging 1.5 mg. or about 0.5 mg. per kilo; they are increased in the same manner as above.

THE TEMPERATURE TAKING.

Injections are usually made in the late forenoon, temperature records being started at the usual three PM. hour and continued at four-hour intervals for forty-eight hours, giving thirteen records over two days, a time period presenting two complete cycles of diurnal variation. This was found necessary because certain cases do not react during the first day. Explanation of this was sought in the nature of the lesion but could not be found further than that mild early lesions may give it but it cannot be read as indicative of low activity since one case of laryngeal tuberculosis had this “delayed reaction.” At times it has seemed to occur when the injection fluid formed a blister under the skin, a pocket in the areolar subcutaneous tissue, whence absorption would be slow. Whatever the correct explanation, experience has justified the recording of temperatures for full forty-eight hours.

THE REACTION.

The experience gained with these monkeys supported definitely the general opinion that tuberculin injected into healthy animals will not disturb the temperature but will produce decided changes in that of tuberculous animals. The reaction in the tuberculous animals may assume several characters, of which usually two are combined in a chart. The commonest and most convincing is a definite rise in the first twelve hours, amounting to one degree or more; rarely it may be three degrees (W). This is followed either by a maintenance of a high level or an attempt to perform the night drop. It may be said that in general there is an abortive attempt in nearly all tuberculin reactions to simulate the V of the normal cycle; this can be seen in charts M, N, O and P. Another rise may be attempted during a similar period of the second twenty-four hours or the whole course may at that time approximate the normal. A modification of this type of reaction is the performance of the whole daily rhythm on a high level, set, as it were, by the initial three PM. record. This form is confusing at times and has been responsible for at least one of our mistakes. Combined with this high level of curve is a tendency for the second twenty-four hours to be higher than the first day (See Variegated Cebus Q and Sooty Mangabey R and Chacma Baboon W). The second type of reaction, illustrated by chart S, fails to resemble the normal daily cycle of the monkey temperature but has sudden rises and falls as its characteristic feature. We have learned to look with suspicion on all charts with sudden marked changes of record even if they follow in the main a rhythmic course. The sudden fall exhibited by a very sick monkey illustrated by Grivet Monkey (T) and Campbell’s Monkey (U) is a bad sign. It has been met more often in advanced caseous pulmonary tuberculosis than in any other tuberculous lesion. On two occasions it has been seen in the absence of tuberculosis so that retest is indicated if the specimen be valuable; such animals however rarely survive the disturbance incident to the test as they are usually suffering with some serious disease. Illustrative charts of several positive reactions serve to elucidate their character better than description. If comparison and contrast of the normal and post- injectional temperature be made, the conclusions are definite.

It cannot be said that any type of reaction indicates a particular form of disease although the last type, the falling of the temperature beyond the thermometric registration point, usually means advanced lesions especially of the caseous pneumonic form. A very small lesion may give a definite reaction as in Cebus (V).

The examples given are those of a definite character but there are many charts that vary from the normal upon which a decision is extremely difficult to make. Such animals are held in quarantine to be retested after the lapse of three months. Early in the work a suspected specimen was reinjected after two weeks, failed to give a reaction but died in about two months of tuberculosis. The nullification of the test by previous injections of tuberculin is well known. Three months’ interval permits a disappearance of the non-sensitivity and allows any latent tuberculosis, possibly stimulated by the toxin, to develop. Repetition upon the same monkey has occurred as high as ten times without apparent harm.

There are sometimes in human beings local reactions at the point of injections. These have been entirely lacking from our monkey specimens. Nor have we ever seen secondary tuberculous lesions appear at the point of the needle-stick. Aseptic syringes and generally cleanly technique have also protected against local abscesses. When an animal is injected he may scratch or pick at the spot for a minute or two but thereafter seems to ignore it entirely.

RESULTS.