I 82 TUBERCULOSIS 



There seems to be no reason for doubting that the bovine and 

 human forms are varieties or races of the same species. The 

 difference in the conditions of life under which they exist in 

 the bodies of men and of cattle are quite enough to explain 

 resulting differences in the bacteria. 



§ 142. Symptoms. The symptoms vary according to 

 the course of the disease. There is a chronic form, which is 

 most common, and an acute form or miliary tuberculosis. 



The symptoms of chronic tuberculosis depend upon the 

 location of the lesions and their extent. When the lesions are 

 situated deeply and are not of great extent, they may not 

 exhibit visible evidence of their presence. In such cases, the 

 infected animal may present the picture of perfect health and 

 show no disturbance of function. Indeed some animals, in 

 which the lesions are both extensive and widely distributed 

 and which have never presented noticeable signs of the disease, 

 are slaughtered for beef without a suspicion of the presence of 

 tuberculosis until they are examined post-mortem. 



inoculated by removing the cap. With sufficient opportunity for the 

 interchange of air little evaporation takes place, and contamination of 

 the culture is of very rare occurrence. In inoculating these tubes, bits 

 of tissue, which include tuberculous foci, especially the most recent, 

 are torn from the organs and transferred to the serum. Very little 

 crushing, if any, is desirable or necessary. I think many failures are 

 due to the often futile attempts to break up firm tubercles. Nor 

 should the bits of tissue be rubbed into the surface, as is sometimes rec- 

 ommended. After a stay of several weeks in the thermostat, I usually 

 remove the tubes and stir about the bits of tissue. This frequently is 

 the occasion for a prompt appearance of growth within a week, as it 

 seems to put certain still microscopic colonies in or around the tissue 

 into better condition for further development. The thermostat should 

 be fairly constant, as urged by Koch in his classic monograph, but I 

 look upon moisture as more important. If possible, a thermostat should 

 be used which is opened only occasionally. Into this a large dish of 

 water is placed, which keeps the space saturated. Ventilation should 

 be restricted to a minimum. As a consequence, moulds grow luxuri- 

 antly and even the gummed labels must be replaced by pieces of stiff 

 manila paper fastened to the tube with a rubber band. By keeping the 

 tubes inclined, no undue amount of condensation water can collect in 



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