DISEASES OF CATTLE 273 



What Favors Its Spread in the Herd? The rate of spread in 

 the herd is dependent on the number of tubercular animals and the 

 number of tubercle bacilli ejected by them. One diseased animal 

 often suffices to infect the healthy part of the herd, but with a 

 larger number of diseased animals in a herd the spread is more 

 rapid. The condition of the herd as to general health, exerts an 

 influence on the rate of spread of tuberculosis. Good and abun- 

 dant feed, proper ventilation and sunlight are conducive to health 

 and retard the spread of the disease in a herd. But tuberculosis 

 may, nevertheless, spread rapidly amongst cattle that are kept con- 

 tinually out of doors. No conditions, however sanitary, will save 

 a herd constantly exposed to infection from animals giving off 

 tubercle bacilli. 



Can Healthy Cattle Become Tubercular If Kept in Unsanitary 

 Stables? Tuberculosis of cattle cannot develop without two nec- 

 essary conditions: First, a susceptible host, the cow; Second, the 

 tubercle bacillus. Both factors are absolutely essential to the oc- 

 currence of the disease. Bad sanitary conditions favor the spread of 

 tuberculosis, but never cause this disease. 



Can the Tubercle Organism Occur and Develop Outside of the 

 Body of the Animal? Owing to the fact that the tubercle bacillus 

 is a parasitic organism, living upon the body juices, and at the 

 temperature >of warm blooded animals, it cannot multiply and de- 

 velop under conditions such as occur in nature, outside of the 

 bodies of animals and men, but it is capable of remaining alive for 

 an unknown time, depending upon conditions, such as moisture, 

 light, etc. 



Does a Tubercular Animal Show Physical Signs of the Dis- 

 ease? It is often thought that a tubercular animal should show 

 physical signs of illness and that the disease should be detected by 

 a careful examination. Such is not the case; even the most ex- 

 perienced and careful veterinarian cannot be certain by a physical 

 examination whether an animal is tubercular or not. This is es- 

 pecially true when the disease is not widely distributed in the 

 body, but even when the lungs and other internal organs are badly 

 affected, it cannot usually be detected by a physical examination 

 of the living animal. If the lymphatic glands that can be felt from 

 the surface of the body are enlarged, or if the animal is so dis- 

 eased that the normal functions of the body are disturbed, the dis- 

 ease can be detected by physical examination. 



A badly diseased animal loses flesh, the coat becomes rough, 

 the eyes dull and staring, and there is a general appearance of lack 

 of vitality. Since in this stage the lungs are almost certain to be 

 involved, the animal may cough, especially after exercising. 



No reliance, however, can be placed on the occurence of phy- 

 sical symptoms, (1) because there are many other troubles that 

 produce the same symptoms, and (2) because in the beginning 

 stages, and often in the more advanced stages, no symptoms what- 

 ever appear. The animal may be apparently in perfect health and 

 have a good flow of milk, and yet be a constant source of danger. 



