Bovine Tuberculosis. 109 



body. This may be accomplished by direct contact of an infected 

 with a healthy animal or by the bacilli being left in a manger, watering- 

 trough, or elsewhere by a diseased individual and later, but before 

 they die, being taken up by a well animal. Thus a barn containing 

 tuberculous cattle will become infected, and healthy animals placed in 

 such a barn before it is properly disinfected are very liable to contract the 

 disease. It is often said, that badly ventilated and poorly kept barns and 

 improper food cause tuberculosis. This is not the case. The disease 

 cannot develop in the absence of the tubercle bacillus, any more than corn 

 can grow in a field in which no corn has been planted. It is, however, 

 undoubtedly true that in poorly ventilated, dirty barns, the tubercle 

 bacilli may be distributed more rapidly than in sanitary stables, but poor 

 air and filth cannot of themselves produce tuberculosis. 



In considering, from a practical point of view, an infectious disease 

 like tuberculosis, one must take into account several important features : 

 (i) the cause, (2) the method of infection, (3) the period of incubation, (4) 

 the dwation of the disease, (5) the zcay to detect or diagnose it, (6) the 

 zvay to control it. There are two other points of interest, namely: (7) 

 the status of the disease in the cattle in New York State and (8) the 

 necessity for experimental work in order to learn more about the disease. 



I, Cause of tuberculosis. 



Tuberculosis is caused by the bacillus of tuberculosis. It is a very 

 small rod-shaped micro-organism. It is so minute that ten thousand of 

 them might be placed end to end within the linear distance of an inch. 

 This organism has a peculiar property of retaining the stain used for 

 coloring it, so that it is possible to distinguish it from other bacteria by a 

 microscopic examination. It will kill guinea pigs when a very few of the 

 bacilli are injected into the subcutaneous tissue. It is also fatal to other 

 animals. The tubercle bacilli that produce tuberculosis in cattle differ 

 very slightly from the bacilli that cause tuberculosis in man, but it is 

 known that they belong to the same species. The Royal Commission on 

 Tuberculosis, appointed by the King of England in 1901, has made in- 

 terim reports in which it states that it has been unable to find any differ- 

 ence in the disease-producing power of the bacilli from certain human 

 and from bovine sources. Other investigations tend to show that the 

 bovine variety of tubercle bacteria is not found in a very large number of 

 tuberculous people. 



This bacillus seems to be able to live for some time in dark and damp 

 places. It is readily killed with a five per cent solution of carbolic acid, 

 or a I to 1,000 solution of corrosive sublimate. Sunlight and drying are 

 not favorable to its existence outside of the body. 



The tubercle bacilli escape from the diseased animal in the saliva and 

 mucus from the mouth when the lungs or certain glands are discharging 



