GENUS BACTERIUM 251 



lous sputum or tissue. 14 Both Nocard and Johne, however, 

 report producing the disease in fowls with human and bovine 

 tuberculous material. Natural infection seems to take place 

 through the respiratory and digestive tracts. There is a pro- 

 nounced difference of opinion 15 as to the relative frequency 

 of infection by these channels. 



Toxin. Bact. tuberculosis produces what seems to be an 

 endotoxin or bacterial protein. As the filtrate of the glycerin 

 bouillon' cultures possesses the property of causing a reaction 

 when injected into tuberculous animals, it is possible that these 

 organisms actually secrete one or more soluble toxins. It is 

 supposed that the endotoxin or toxines give tuberculin its 

 value. 



Tuberculin. Tuberculin consists of the liquid (usually 

 glycerinated bouillon) on which tubercle bacteria have grown 

 for several weeks, after it has been heated to kill the bacteria 

 and filtered to remove all of the organisms and properly con- 

 centrated. It was discovered by R. Koch in 1890. 16 The 

 original tuberculin was prepared by evaporating the filtrate 

 of cultures of tubercle bacteria of sufficient age to one-tenth of 

 the original quantity. This gave a thick syrupy fluid that had 

 to be diluted before use. It is known as the crude tuberculin 

 and was originally called Koch's "lymph." There are several 

 modifications of the details in its preparation. It can be pre- 

 pared either from the human or bovine variety of tubercle 

 bacteria. Our experience has not pointed to any pronounced 

 difference in the action of the tuberculin prepared with cul- 

 tures from either source. In the preparation of tuberculin 

 (old tuberculin of Koch) the following principles 17 should be 

 observed. 



1. "The medium shall consist of bouillon prepared from 



14 Moore. Jour, of Med. Res., Vol. XI (1904) p. 521. 



15 See article by M'Fadyean. Jour, of Comp. Path, and Therap., 

 1910. 



1G Koch. Centralbl. f. Bakt., 1890. 



"Report of Committee on the Standardizing of Tuberculin. 

 Laboratory Section, Am. Public Health Association, 1908, 



