TUBERCULOSIS IN ANIMALS, AND ITS RELATION TO CONSUMPTION IN MAN.

Otago Witness, Issue 1916, 30 October 1890, Page 6

TUBERCULOSIS IN ANIMALS, AND ITS RELATION TO CONSUMPTION IN MAN.

( Conoludd.)

In reference to the pathological study of tuberculosis it is stated that the experimental and bacteriological investigations date back only comparatively a few years. In 1843 Klencke came to the conclusion that tuberculosis was due to a specific virus — was, in fact, a contattious disease ; but it was not until 1865, when Villemin established the results of experiments which showed that this disease could be transmitted from man to animals by inoculation, that this view of its nature began to be generally adopted. Gerlach's experiments in 1866-69 confirmed the results of Klencke'n previous investigations. In 1869 Chauveau began a series of observations with the object of ascertaining, whether tuberculosis could be induced by feeding Animals with tuberculous material, and alsoif it was possible to produce the disease in animals by the inhalation of the dried and finely -.palvirised sputum of consumptive patients. From these experiments, which were of a very comprehensive nature, Chauvean came to tho conclusion that the disease could be readily contracted by both ingestion and inhalation. M. St. Cyr, of Lyons, in 1873-74, confirmed the conclusions previously arrived at by Chauveau. It had thus been proved experimentally that tubercle could be conveyed from' man to animals and from animal to animal in three, .ways — viz., by inoculation, ingestion, and inhalation. In addition it bad also been held for some time previously— as the result of practical experience, the opinion of medical menand breeders of stock — thit this disease is hereditary. The next great advance in the study of tbe disease was in 1881, when Toussaint made the discovery that the virus could becultivated apart from .any animal body. In the following year Eoch discovered in tubercular deposits the constant existence of a rod-shaped body, which he considered the true cause of the disease, and named it the " tubercle bacillus." Koch's discovery was inquired into, and soon generally accepted. A method was thus established of determining whether any morbid deposit in the lungs or other organs of man or animals was tubercular in its nature or not.. It is true that more recent and extended bacteriological investigations show that this tubercle bacillus of Eoch cannot be distinguished at tho present time by any of the known tests from the bacillus of leprosy, or from the bacillus recently described by Lin gar d in the affection known as lupus in the face of the human subject ; but as these diseases are totally different in their ordinary clinical characters from tubercle, there is not much danger of their being confounded with it.

Prior to these experimental investigations and the discovery of the bacillus by Koch, tuberculosis was supposed to be due to various causes, among which may be mentioned climatic influences, defective nutrition, exposure to hardships, excessive secretion — in fact, any and every influence calculated to produce debility. Since Koch's discovery these alleged causes have been considered as only predisposing or preparing the structures of the body for tho reception of the disease-producing germs which are the true cause. Whatever may be the part played by debilitating influences in the production or progress of tuberculosis, Dr Ransome has recently shown that,' among people in communities where such influences are general and continuous, consumption is far more prevalent than in others where such influences are not at work. Heredity has always been looked upon as a cause of tuberculosis, but thiß has, as already stated, been the result of practical observation rather than of scientific inquiry. It is difficult to say in what way heredity operates as a cause of disease. It may possibly be on the generallyaccepted principle that like produces like, and in this case the consumptive offspring of consumptive parents is only an example of a general natural law. On the other hand, direct infection may occur before birth ; the tubercle bacillus may be transferred from the parent to the foetus. Professor Johne, of Dresden, found in an eight-months calf caseous nodules containing tubercle bacilli ; it has also been said that the organism may be transferred to the ovum at the time of impregnation. Breeding-in-and-in has long been accepted as an important factor in the transmission of tubercle, but this view is untenable in face of tbe evidence that can be furnished by well-known breeders of pedigree stock. Breeding-in-and-in so long as healthy stock are used will never produce tuberculosis, but if tainted animals are used for the in-breed-ing, then the hereditary taint will be more and more intensified. Until quite recently it was generally accepted that of our domesticated animals cattle were the only victims of this disease, and therefore the only ones from whioh man may become affected through the use of their flesh as food, but it is now known that fowls are more frequently attacked than any other animals. Experiments have shown that rabbits and guinea pigs are also very susceptible. Pigs are not uncommonly affected, sheep and goats are occasionally attacked, and the malady now appears to be more common in the horse than was suspected two or three years ago. From what has been stated it may be inferred that in many oases there is great difficulty in deciding whether »n animal is the subject of tuberculosis or not. Cattle may have tubercular deposits in their lungs and other organs, and still manifest all the appearances of perfect health. Butchers are now well aware of thif, and in some legal proceedings instituted recently where tubercular carcasses wore seized and destroyedj the purchteers produced proof that they bought the cattle aa sound animals, and paid a price which they would only have given on the condition or in the belief that they were healthy. They also showed that, as the beasts were in fine condition, they had no means of knowing that th*> disease existed until after slaughter, when the internal organs were aze,«

mined and the carcasses seiSed. in other cases tuberculosis is marked by well-defined symptoms in its progress. These are : a cough which may not at first attract the owner's attention until the breathing becomes altered m oharaofcer and laboured. Accompanying this cough there is always a general unthrifty appearance, gradual emaciation (wasting), and an irregular or capricious appetite. There may be some external manifestations of the disease visible, such as enlargements the glands of the throat, and in the case of milch cows hard nodular deposits may in advanced cases be found in the udder. The question has been often asked, How fat and to what extent is tuberaulosis contagious? Even at the present time, although the disease Las been produced experimentally by iuoculation, inhalation, and ingestsioa, many people do not believe ia its contagious nature— at least not in the ordinary sense. Many cases are, however, recorded in the human subject of consumptive patients affecting other people with whom they were in the habit of daily associating. But in consumption hospitals the nurses are daily and constantly exposed to the risk of infection in this way } the tubercle bacillus h»s been found abundantly in the air of the hospital wards, but still it is the exception to find the Burses fall victims to this disease. It must be admitted therefore that the infective power of consumption in man is very low. In a similar manner the infective power of tubercle in animals is^ very low. It may happen that one or two animals in a herd may be affected with tubercle and gradually waste, until the owner either kills them and buries tho carcass, or sells the animal to the jobber for about; the value of the hide ; yet no apprehension is felt with regard to the rest of the herd, and tho evidenoe of practical men is that tubercle does not spread like other contagions diseases. In cattle as well as in man the surrounding circumstances have often muob. to do with the extension of the disease.

The ingestion of tubercular matter by an'mals has proved the means of inducing the disease, and from this the question naturally arises whether the flssh or milk of all tuberculous animals should be condemned as dangerous and unfit for human food. There is great diversity of opinion on this point, for while some maintain that the flesh aud milk of all such animals should bo destroyed, others hold thit if the lesions are localised and confined to the lungs, the meat and milk may be used without danger. Meat is always cooked before b-iing used as human food, and ib has been demonstrated by Koch, Lingard, aud others that a boiling temperature for a few minutes is sufficient to destroy the vitality and infective power of the bacillus ; but milk is generally used as food without cooking, more especially in the oase of children.

Tuberculous milk must therefore be looked upon as dangerous, and likely to be the means of producing the disease ia young or weakly Bubjects consuming it. The chief difficulty in determining whether the milk of any particular cow is dangerous lies in the inability of the veterinary surgeon to say whether there are any tubercular deposits in the udder. Milk may contain these organisms, and even a skilled bacteriologist fail to find them ; their absence in the few drops which he examines is no guarantee that; they may not exist. Recent experiments in America have demonstrated that where tub -.rculous cows showed no signs of disease in the udder, their milk proved infective to rabbit* and guiuea pigs fed with it. The results of the feeding experiments all tend to prove that milk from tuberculous cows, if given in the uncooked state, possesses a much higher infective power than tha flesh.

The following, which appeared in the Lancet of August 30, received by last mad, fully justifies the apprehensions of the dangers of infection by the use of milk from tuberculous cows:— "Dr Oarl Hirsohbergei has made, at the request of Dr Bollinger, a series of experiments in tha Pathological Institute at Munich on the inoculation of animals with the milk from cows in various stages of tuberculosis. He attempts to answer the following questions— (l) Do tuberculous cows frequently give infectious milk, or is their milk only exceptionally infectious? {3) In worst forms of tuberculosis is the milk infeotious, and is it so in localised, or only in general tuberculosis? He made 2o experiments, and calls attention to the fact that inooulation alone can give decisive results, because it is very difficult to observe tuborcle bacilli microscopically in the milk, and impossible to discover the BporeH. On tho strength of his experiments he states that the clanger from infection from the milk of tuberculous cows does not only exist, but is very great, being found in 55 per cent, of all cases examined. The more the tuberculosis has spread the greater is the danger ; but even in mild cases of tuberculosis the disease is, he considers, more or less infectious."

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