694 ANNUAL REPORT- OF THE Off. Doc. 



the universal pioininence f,nven to sanitary conditions as predispos- 

 inj^ causes they are almost entirely ignored among the prophylactic 

 measures suggested by many of these same authorities. 



The following investigation was made to show that tuberculosis 

 is infectuous: 



For this purpose two herds were established of six cows each. 

 Four cows in each herd were healthy, and two cows in each herd were 

 tubercular. One herd was kept in a roomy, light, clean and well 

 ventilated stable. The stalls and partitions between the mangers 

 in this stable were so constructed tliat the cows were kept apart 

 from each other. The other stable was small, close, poorly ven- 

 tilated, rather dark and not especially clean. The cows here were 

 not separated by stall partitions and they were all fed from the floor 

 of the passageway in front of their stalls. This experiment con- 

 tinued for 513 days or about 17 months, and at the close it was 

 found that two t)f the originally healthy animals kept in the large, 

 clean, light stable had contracted tuberculosis and the other two of 

 the originally healthy cows continued sound. Of the four original 

 cows in the small dark stable, all had contracted tuberculosis. The 

 progress of the disease in each infected animal in the dark stable 

 was greater than in the infected animals in the light, airy stable. 



It is concluded from this experiment, that — 



1. Good sanitary conditions, cleanliness and the comparative isola- 

 tion afforded by separate mangers and by stall partitions, have a 

 decided effect in restricting the spread of tuberculosis in an infected 

 herd. 



2. A poorly ventilated and poorly lighted stable and one in which 

 the cattle come into direct contact, as is the case when there are no 

 partitions between the stalls and mangers, is favorable to the spread 

 of tuberculosis in an infected herd. 



3. However good the construction and sanitary conditions of the 

 stable and however good the care of the animal may be, the spread 

 of tuberculosis cannot be altogether prevented if tubercular cattle 

 and healthy cattle are kejjt in the same stable. 



Tuberculosis always begins as a local disease at the point at which 

 the tubercle bacilli are arrested and grow'. The location of the point 

 of primary infection depends largely upon the channel of infection. 

 If the germs have been inhaled, disease is most liable to start at 

 some part of the respiratory tract. If the germs have been taken in 

 with the food or water, disease is liable to start at some part of the 

 digestive tract, usually in the throat, small intestines, liver or me- 

 senteric lymphatic glands. If infection is through the skin, tuber- 

 culosis will first form at the point of inoculation. 



If the cow is infected by a tubercular male the disease will origi- 

 nate in the uterus. Sometimes tubercle bacilli are carried a certain 

 distance from the port of entrance before they lodge and commence 

 to multiply. Until recently it was denied that the tubercle bacilli 

 could thus be carried from the point at w^hich they are introduced 

 without leaving an area of disease at that place, but it is now known 

 that these germs may pass through the lungs and not cause discover- 

 able disease they reach the bronchial or mediastinal lymphatic 

 glands. Similarly, tubercle bacilli may pass through the wall of the 

 pharynx and j)roduce no alteration of structure until they arrive in 

 the most postpharyngeal lymphatic glands. It may be, and there 



