The most frequently used method of testing is the subcutaneous test, which consists in injecting the proper quant.i.ty of tuberculin underneath the skin into the subcutaneous tissue. If an animal is tuberculous, the action of the tuberculin causes a fever, which is indicated by a rise in temperature.
This rise, under ordinary conditions, may occur any time between the eighth and twentieth hours after the tuberculin is injected, but in some cases it is desirable to measure the temperature before the eighth hour and continue to the twenty-fourth hour or longer.
The temperatures are measured at least 3 times in advance of the injection, at 2-hour intervals, to learn whether the animal is in proper condition to receive the test. The temperatures after injection are taken every 2 hours until the test is completed. The proper interpretation of the temperatures is made by the person applying the test, and a careful observance of any clinical changes is always important in determining the result. It can not be set forth too strongly that the test, including the two following methods, should be attempted only by those who are properly qualified to do the work.
THE INTRADERMIC TEST (INTO THE SKIN).
The intradermic test for detecting tuberculosis is used to a considerable extent, especially in area work and on range cattle not easily controlled.
When made by those who have become skilled in its application, it is very accurate. In this test the tuberculin is injected between the layers of the skin, only a few drops being used, and it is usually applied in the region at the base of the tail, where the skin is soft and nearly hairless. The intradermic test is satisfactory also for the diagnosis of tuberculosis in swine and, when so used, the tuberculin is applied into the skin of the ear near its base.
The reaction from the intradermic test consists of a swelling at the point of injection and is observed from 72 to 150 hours after the injection. The character of the swelling varies, and a proper diagnosis of tuberculosis by this test can be made only by an experienced person.
THE OPHTHALMIC TEST (INTO THE EYE).
Still another method, known as the ophthalmic test, is used quite frequently and has been found to be of considerable value in what is known as "check" testing; that is, it is used in connection with either of the previously described methods. Sometimes a tuberculous animal that fails to react to those tests shows evidence of the disease upon the application of the ophthalmic test. The ophthalmic tuberculin is placed in one eye and the other eye is used as a check. A reaction is indicated by a characteristic discharge from the eye receiving the treatment, which may occur in from 3 to 10 hours after the application or even later. Some swelling and inflammation of the eye and lids are often noted.
TREATMENT OF TUBERCULOSIS.
Treatment of the disease is not seriously considered by any authorities at the present time.
The measures to be adopted to prevent the spreading of the disease must take into consideration not only the tubercle bacillus, but likewise all those circ.u.mstances that make cattle more susceptible to the disease, and which have already been dwelt upon. It would be useless to repeat here all that has been said above on the transmission of tubercle bacilli from one animal to another, and on the dangers of certain debilitating influences. A careful study of these influences will show how tuberculosis may, at least in some cases, be prevented. Great care should be bestowed upon the breeding, the surroundings, and the feed of the animal, so that the latter may be put into a condition to resist infection even when exposed to it. A tuberculin test should be applied to all strange cattle before they are introduced into the herd, and those which show a reaction should be refused.
A rigid exclusion of tuberculous animals is all that is necessary to prevent the appearance of the disease, provided cattle are not infected by consumptive persons and animals. The transmission of the disease from man to cattle is probably not frequent, but is regarded as a possible source of infection.
Tuberculosis in cattle must also be considered as bearing upon tuberculosis of other domesticated animals, particularly hogs. In Europe and the United States this disease is not uncommon among hogs, and appears to be on the increase. The reason for its existence may be looked for in the feeding of pigs with skim milk, b.u.t.termilk, and whey from creameries, with the offal of the abattoirs, with the household refuse generally, and behind tuberculous cattle. If tuberculosis is common among cattle, it is likely to be transmitted to hogs kept in this way.
The carca.s.ses of animals which have died of tuberculosis should be buried deeply so that they can not be eaten by other animals. This is likewise true of all organs or tissues of slaughtered animals containing tubercles.
These should never be fed to other animals, such as hogs, dogs, and cats, and should either be destroyed by fire or deeply buried.
When any of the animals in a herd of cattle show evident symptoms of tuberculosis, or when the tuberculin test proves that they are affected with this disease, the best method of procedure in most cases is to have the affected animals slaughtered and the stables disinfected. A large proportion of the animals which are slightly affected yield carca.s.ses which are perfectly wholesome and fit for human food, but in all such cases there should be an inspection by an expert at the time of slaughter to determine which carca.s.ses may be used and which should be destroyed.
The disinfection of stables may be accomplished by thoroughly cleaning them, scrubbing the floors with hot water, brushing down all loose dust from the walls, and tearing off all woodwork which is partly decayed. Then the whole interior of the stable should be covered with a good coat of limewash containing 1 part of formalin (which is a 40 per cent watery solution of formaldehyde) to 30 parts of the lime wash, or 4 ounces of formalin to each gallon of lime wash.
Similar precautions should be observed in removing the manure of the infected herd from the barnyard and other places accessible to cattle, since it is known that tuberculous cattle frequently eliminate large numbers of tubercle bacilli through the feces. The ground under the manure pile should then be disinfected, either by the above-mentioned formalin solution or by unslaked lime thickly sprinkled over the soil.
If all the animals which react are destroyed and the stables disinfected in this manner, the herd should remain free from the disease unless other affected animals are added to it. The introduction of the disease in this manner may be avoided by requiring a tuberculin test of all new animals admitted on the premises.
Unfortunately it is a fact that tuberculous animals which have been tested several times may become so accustomed to tuberculin that they will no longer react; consequently it is always advisable to purchase cattle from some one who is known to be reliable, as otherwise animals of this kind may be treated with tuberculin for the purpose of hiding the disease.
In the case of very valuable purebred animals and under exceptional circ.u.mstances it may be more advantageous to retain the reacting animals which are in good condition in order to breed from them and in that manner avoid the excessive loss which would follow from their immediate slaughter.
This may be done if proper precautions are adopted.
The disposal of reactors depends upon the State laws and live-stock regulations of the State in which the herd belongs. If this policy is followed it should be attempted only after careful study of the plan known as the Bang method of controlling tuberculosis. The live-stock officials of the State should be frequently consulted and their advice followed; otherwise failure will surely ensue. The plan necessitates considerable trouble and is not recommended except under the circ.u.mstances mentioned.
BOVINE TUBERCULOSIS AND THE PUBLIC HEALTH.
The increasing amount of evidence pointing to the ident.i.ty of human and animal tuberculosis, combined with the extraordinary mortality of human beings from this disease, often amounting to 10 to 14 per cent, has raised the question in all civilized countries as to how far animal, and especially bovine, tuberculosis is to blame for this high mortality. The medical and veterinary professions have approached this problem with equal zeal, and much has come to light within recent years which enables us to come to some conclusion. If this disease is transmitted from animals to man, how does the transmission take place? As comparatively few people come in direct contact with tuberculous cattle, it must be either through the meat, the milk, the b.u.t.ter, the cheese, or through all these products that the virus enters the human body. The question has thus narrowed itself down to the food products furnished by cattle.
It has become a very urgent question, especially in the poorer countries of Europe, whether all flesh from tuberculous animals is unfit for human food.
It is argued there that if it can be shown that in the majority of cases of tuberculosis the bones and the muscular system are free from infection, there is no reason why the meat should not be put on sale under certain restrictions. The question may be resolved into two divisions: (1) How frequently does the disease invade those parts of the body which are used as food? (2) When the disease process is manifestly restricted to the internal organs, do tubercle bacilli circulate in the blood and lymph and can they be detected in the muscular tissue?
(1) Disease of the bones is not unknown, although very rare. According to Walley, it appears chiefly in the spongy bones of the head and backbone and in the long bones of the limbs. Occasionally the ends of the bones, where they are covered by the synovial membrane of the joints, are dotted with tubercles. The muscular system itself is very rarely the seat of tuberculous deposits, although the lymphatic glands lying near and among the muscles may be not infrequently diseased.
(2) Whether tubercle bacilli are found in muscle juice independent of any tuberculous deposits is a question which must be approached experimentally.
There is on record a great variety of opinions on this matter, some authorities considering all flesh from tuberculous animals unfit for food, while others hold a contrary view. Experiments have shown that in rare cases the flesh of tuberculous cattle contains a small number of tubercle bacilli. In Germany the flesh of animals in which the disease is just beginning, or in which it is restricted to one or more related organs, is not rejected. When, however, the disease has affected the muscles or bones, or lymphatic glands situated on or between them, the flesh is condemned as unfit and dangerous. Animals are also rejected in which it is evident, from the general distribution of tubercles throughout the various organs, that the bacilli have been distributed by the blood and may have been carried into the muscular system (generalized tuberculosis).
Concerning the infectious nature of milk secreted by tuberculous cows, authorities have universally agreed that when the udder itself is in the slightest degree involved the milk possesses infectious properties, and is therefore dangerous. Tubercle bacilli in large numbers have been found in the milk and the udder under such circ.u.mstances. Unlike other affections of the udder, tuberculosis of this organ does not at once change the appearance and the quality of the milk secreted. Bang states that for at least a month after the disease has appeared the milk is normal in appearance and may be consumed and sold without arousing the suspicion of the owner. Considerable danger is, therefore, involved in this disease, and the necessity for the careful inspection of dairy cows seems more urgent than ever.
Authorities are, however, not fully agreed as to whether the milk from tuberculous cows in which the udder is apparently not invaded by the disease should be considered dangerous or not. Some incline to the belief that the milk secreted by healthy udders is never infectious, even when the lungs or other organs are affected; that, in other words, the tubercle bacilli are rarely, if ever, separated from the lesions which they produce, and that the udder itself must be diseased before tubercle bacilli can appear in the milk. Experiments made with the milk of tuberculous cows in which there were no indications of udder disease do not bear out this theory, since tubercle bacilli have been found in their milk. Some authorities still believe that the udder is diseased when the milk is infected, but that the disease escapes observation. However this may be, the fact that the udder may be diseased and the disease not recognizable simply casts suspicion upon all milk from tuberculous animals. We know that the milk of tuberculous cattle may or may not contain tubercle bacilli when the udder is apparently free from disease, but we have no rapid method of determining whether in any given case the milk contains tubercle bacilli or not. Moreover, the bacilli may be absent at one time and present at another in milk from the same cow. When we consider, therefore, the extent of tuberculosis and the hidden character of the disease, a certain degree of suspicion rests upon all milk from untested cattle. Fortunately, tubercle bacilli are readily destroyed by the temperature of boiling water, and hence both meat and milk are made safe, the former by the various processes of cooking, the latter by boiling for a few moments. It is inc.u.mbent upon all communities to have dairy cows examined and tested with tuberculin. If disease is detected, the affected animal should be killed at once or else all opportunity for the sale of such milk removed by appropriate measures.
Where milk or cream is sold to the trade in large towns or cities pasteurization should be required as an additional safeguard.
Recently there has been much discussion of the question as to whether human and animal tuberculosis are identical diseases and as to the possibility of the tuberculosis of animals being transmitted to man or that of man being transmitted to animals.
The fact that tuberculous material from human subjects often failed to produce serious disease in cattle was observed by a number of the earlier investigators who experimented with such virus. It was the experiments and comparative studies of Theobald Smith, however, which attracted special attention to the difference in virulence shown by tubercle bacilli from human and bovine sources when inoculated upon cattle. Smith mentioned also certain morphological and cultural differences in bacilli from these two sources, and in the location and histology of the lesions in cattle produced by such bacilli. He did not conclude, however, that bovine bacilli could not produce disease in the human subject, but said:
It seems to me that, accepting the clinical evidence on hand, bovine tuberculosis may be transmitted to children when the body is overpowered by large numbers of bacilli, as in udder tuberculosis, or when certain unknown favorable conditions exist.
Koch, however, in his address at the British Congress on Tuberculosis, went far beyond this and maintained that "human tuberculosis differs from bovine and can not be transmitted to cattle." As to the susceptibility of man to bovine tuberculosis, he said it was not yet absolutely decided, but one was "nevertheless already at liberty to say that, if such a susceptibility really exists, the infection of human beings is but a very rare occurrence." He emphasizes this view in the following language:
I should estimate the extent of infection by the milk and flesh of tubercular cattle and the b.u.t.ter made of their milk as hardly greater than that of hereditary transmission, and I therefore do not deem it advisable to take any measures against it.
This conclusion was so radically different from the views of most experimenters and so out of harmony with facts which had apparently been demonstrated by others that it at once aroused opposition in the congress, followed by the adoption of dissenting resolutions, and led to numerous investigations in various countries. Koch"s conclusions were based upon his failure to produce tuberculosis in cattle and other animals by inoculating them with tuberculous material of human origin and his success in causing progressive and fatal tuberculosis in the same kinds of animals when inoculated with tuberculous material of bovine origin. With such positiveness did he hold to the constant and specific difference between the human and bovine bacillus that he promulgated an experimental method of discriminating between them. Speaking of the etiology of intestinal tuberculosis in man, he said:
Hitherto n.o.body could decide with certainty in such a case whether the tuberculosis of the intestine was of human or of animal origin. Now we can diagnose them. All that is necessary is to cultivate in pure culture the tubercle bacilli found in the tubercular material, and to ascertain whether they belong to bovine tuberculosis by inoculating cattle with them. For this purpose I recommend subcutaneous injection, which yields quite specially characteristic and convincing results.
These important and comprehensive conclusions followed from a comparatively few experiments upon animals, and apparently no effort had been made to learn to what extent human tubercle bacilli may differ in their virulence for cattle or what grades of virulence there might be among bacilli of bovine origin. Vagedes had already shown that bacilli were sometimes present in human lesions which were as virulent as bovine bacilli, but his work was wholly ignored by Koch.
A considerable number of investigators, including Chauveau, Vagedes, Ravenel, De Schweinitz, Mohler, De Jong, Delepine, Orth, Stenstrom, Fibiger and Jensen, Max Wolff, Nocard, Arloing, Behring, Dean and Todd, Hamilton and Young, the German Tuberculosis Commission, and Theobald Smith, have found tubercle bacilli in the bodies of human beings who died of tuberculosis which proved to have about the same virulence for cattle as had the bacilli from bovine animals affected by the disease.
Kossel, in a preliminary report, stated that the German commission had tested 7 cultures of tuberculosis from cattle and hogs--4 from cattle and 3 from hogs. Two proved acutely fatal in cattle after eight to nine weeks; 4 likewise produced a generalized tuberculosis, but which certainly had a more chronic course, while 1 of the cultures caused only an infiltration at the point of inoculation, with some caseous foci in the adjoining prescapular gland and in one of the mediastinal glands, and there was lacking the spreading of the tuberculosis over the entire body which they were accustomed to see after the injection of cultures of bovine tuberculosis. "Hence," says Kossel, "among bovine tuberculosis bacilli there can also occur differences with regard to the virulence."
The German commission also tested 39 different freshly made cultures from tuberculous disease in man. Nineteen did not produce the slightest symptoms in cattle; with 9 others the cattle exhibited after four months very minute foci in the prescapular glands, which were mostly encapsuled and showed no inclination to progress; with 7 other cases there was somewhat more marked disease of the prescapular glands, but it did not go so far as a material spreading of the process to the adjoining glands. There were 4 cultures, however, which were more virulent and caused generalized tuberculosis in the cattle inoculated with them.
It would appear, therefore, that hereafter everyone must admit that it is impossible always to tell the source of a culture of the tubercle bacillus by its effect when it is inoculated upon cattle. One of the bovine cultures failed to produce generalized tuberculosis in cattle, and some of the human cultures did produce it in such animals. Moreover, while some of the human cultures caused no disease at all, others led to the development of minute foci in the prescapular glands, and still others to somewhat more marked disease of the glands. There were, consequently, four degrees of virulence noted in these 39 cultures of bacilli from human sources and three degrees of virulence in the 7 cultures from animal.
Now, if we accept the views of Koch as to the specific difference between human and bovine tubercle bacilli, and that the human bacilli produce only localized lesions in cattle, while bovine bacilli produce generalized lesions in them, must we not conclude that the one non-virulent bovine culture was in reality of human origin, and that the animal from which it was obtained had been infected from man? This is a logical deduction, but reverses the dictum laid down at London that human tuberculosis is not transmissible to cattle. Again, how are we to explain the human cultures of medium virulence? Are they human bacilli which, for some unknown reason, are increasing in virulence and approaching the activity of the bovine bacillus, or are they really bovine bacilli which have multiplied in the human body until their virulence has become attenuated? In whatever manner these questions are decided it would seem that the findings of the German commission, instead of supporting Koch"s views that we can decide with certainty by the inoculation of cattle as to the source of any given bacillus, really show that this method of diagnosis is extremely uncertain in the present condition of our knowledge.
It is definitely admitted that 4 of the human cultures caused generalized tuberculosis in cattle; Kossel suggest, however, that it may be possible that the bacilli in cases of human tuberculosis under certain circ.u.mstances can likewise attain a very high pathogenic activity for cattle without being for that reason bovine bacilli. Undoubtedly the German commission is confronting the two horns of a dilemma, either one of which is fatal to the views of Koch as stated with such positiveness at London. If we accept this suggestion thrown out by Kossel, we must conclude that Koch was wrong in his claim that human tuberculosis can not be transmitted to cattle, and thus with one blow we destroy the entire experimental support which he had for his argument before the British Congress on Tuberculosis. If, on the other hand, we accept the conclusion which follows from the principle laid down by Koch for the discrimination between human and bovine bacilli, and which appears to be favored by Kossel, we must admit that bovine tuberculosis is an extremely important factor in the etiology of human tuberculosis. Of the 39 cases of human tuberculosis tested, 4, or more than 10 per cent, were virulent for cattle and would be cla.s.sified as of bovine origin; however, these 4 cases, were all found among the 16 cases of tuberculosis in children which the commission investigated; hence it is plain that 25 per cent of the cases tested of tuberculosis in children would by Koch"s method be cla.s.sified as of bovine origin.
In the Bureau of Animal Industry two distinct lines of experiments have been carried on, in order that one might serve as a check against the other. There has been, however, no discrepancy in the results. De Schweinitz, in the Biochemic Division, Bureau of Animal Industry, isolated 9 cultures from human tuberculosis. Two were derived from human sputum, 3 from cases of generalized tuberculosis in adults, and 4 from cases of generalized tuberculosis in children. By comparing these cultures with a newly isolated virulent culture of bovine tuberculosis, there were found among them 2 cultures from children which were identical in their cultural and morphological characters with the bovine bacillus. These cultures also killed rabbits and guinea pigs in as short a time as did the bovine bacillus. Hogs which were inoculated subcutaneously with these 2 cultures from children died of generalized tuberculosis. Two calves weighing more than 300 pounds each were inoculated subcutaneously with these virulent human cultures, and as a result developed generalized tuberculosis. A yearling heifer inoculated with 1 of the cultures showed generalized tuberculosis when killed three months after inoculation. Both the cattle and the hogs had been tested with tuberculin and found to be free from tuberculosis before the inoculations were made. It is important to observe in this connection that 2 out of 4, or 50 per cent, of the cultures obtained from cases of generalized tuberculosis in children proved virulent for cattle.
Mohler, working in the Pathological Division, Bureau of Animal Industry, obtained 3 very virulent cultures of tubercle bacilli from the human subject. A goat inoculated subcutaneously with 1 of these cultures died in 37 days with miliary tuberculosis of the lungs involving the axillary and prescapular glands. This bacillus was obtained from the mesenteric gland of a boy. Of still greater interest is a bacillus isolated by Mohler from human sputum. A goat inoculated subcutaneously with a culture of this germ died in 95 days of pulmonary tuberculosis. A cat inoculated in the same manner died in 23 days of generalized tuberculosis. A rabbit similarly inoculated died in 59 days of pulmonary tuberculosis. Another rabbit inoculated with a bovine culture for comparison lived 10 days longer than the one inoculated with this sputum germ. Mohler also inoculated subcutaneously a 1-year-old heifer with a culture derived from the tuberculosis mesenteric gland of a boy 4 years of age. This culture was always refractory in its growth under artificial conditions, and the bacilli were short, stubby rods, corresponding in appearance to the bovine type. At the autopsy, held 127 days after the inoculation, the general condition was seen to be poor and unthrifty, and large, hard tumors were found at the points of inoculation. On the right side the swelling measured 3-1/2 by 5 inches, and the corresponding lymph gland was 2-3/4 inches long by 1-3/4 inches in diameter. This gland contained numerous calcareous foci; one at the apex was an inch in diameter. The lesions on the left shoulder of the animal were very similar to those found on the right side, but the dimensions of the tumor were slightly less. The lungs presented an irregular ma.s.s of tuberculous nodules, and 7 or 8 grapelike nodules were seen on the parietal pleura. Bronchial and mediastinal lymph glands contained numerous tuberculous foci, and the pericardium, peritoneum, spleen, and liver also were affected.
In order to throw some light, if possible, upon the morphological constancy of the different types of tubercle bacilli, Mohler made comparative studies of bacilli from various sources, and which had been pa.s.sed through various species of animals, by making the cultures upon dog serum after the method described by Theobald Smith. Some important results have been obtained. One culture of human bacilli which had morphological and cultural peculiarities similar to those of the bovine bacillus, and which produced only local lesions in cattle, was pa.s.sed through a series of five cats. It was then found to be completely changed in its morphological characters, the rods being elongated, slender, more or less beaded, and entirely of the human type. Far from decreasing in virulence, however, as might be expected from its morphological appearance, this bacillus had so increased in its pathogenic activity that it produced generalized tuberculosis in a cow.
This cow was inoculated subcutaneously in front of each shoulder with 2 cubic centimeters of a salt-solution emulsion of the tuberculous omentum of the last cat of the series. The cow rapidly lost flesh, had a temperature of 104 F., with the point of inoculation and adjacent glands greatly swollen. The autopsy revealed generalized tuberculosis, involving the lungs, mediastinal glands, spleen, liver, and kidneys. Tubercle bacilli of the bovine type obtained from the mesenteric glands of a sheep, hog, and cow were similarly transformed in their morphological appearance after being pa.s.sed through a series of cats and recovered on dog serum. These bacilli also increased in virulence, as the last cat in the series invariably succ.u.mbed in a shorter time than the first of the series.