Bovine Tuberculosis. 149 



multiply there, and by their increase penetrate deeper and deeper 

 into the organs of the body, destroying the tissues as they go. 

 Finally the injured organs give rise to symptoms, at first slight, 

 but gradually they become more and more serious until death is pro- 

 duced, because some organ necessary for the life of the individual 

 has been destroyed. While diphtheria completes its course in a few 

 days or weeks, tuberculosis requires for the same purpose months and 

 more often years. 



It is important that both the specific, and the infectious nature of 

 tuberculosis be understood. It is a "specific" disease because it 

 is produced by a single cause — the tubercle bacillus. It is "infec- 

 tious " because the tubercle bacteria are taken into the body. This 

 may be by direct contact or by the bacilli being left in a manger, or 

 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 wll become infected, and healthy 

 animals placed in such a bam before it is 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 

 com has been planted. It is, however, undoubtedly true, that in 

 poorly ventilated, dirty bams, 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, we must take into account seven important features : 

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

 (4) the duration of the disease, (5) the way to detect or diagnose it, (6) the 

 way to eliminate it, and (7) the methods for preventing it. 



1. Cause of Tuberculosis. 



Tuberculosis is caused by a micro-organism, the bacillus of tuber- 

 culosis. It is a very small rod-shaped micro-organism. It is so 

 minute that 10,000 of them might be placed end to end within the 

 linear distance of a single inch. This organism has a peculiar way of 

 retaining the stain used for coloring it, so that it is possible to dis- 

 tinguish 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 are found in tuberculous cattle and people often differ 

 very slightly from each other, but it is known that they belong to 



