PATHOGENIC BACTERIA. 95 



Nearly all the cases of heredity can be explained in this man- 

 ner. The young children, possessing very little resistance, are 

 constantly exposed to the infection through inhalation and also 

 by nutrition. 



Immunity. No one can be said to be immune, though per- 

 sons who have been greatly weakened would offer less resistance 

 than health}'' individuals. 



Products Of Tubercle Bacilli. The last year has developed 

 some wonderful facts in relation to this important deadly bacillus. 

 In 1889, Dr. Dixon, then Professor of Hygiene at the Univer- 

 sity of Pennsylvania, spoke of a method of curing tuberculosis 

 in guinea-pigs and with products obtained from the bacillus ; 

 not much was thought of this statement at the time. 



In August, 1890, Koch, before the Medical Congress claimed 

 that he also had been able to cure tuberculosis in guinea-pigs, 

 and would be able to give some interesting facts later on. In 

 November he claimed that he had obtained reactions in man 

 similar to those in the guinea-pig, and believed that a cure was 

 at hand. 



In the excitement which followed this statement, the greatest 

 hopes were raised and the impossible expected. In January, 

 1891, Koch made public the manner of preparing the lymph or 

 u Tuberculin" or u Kochin," as it was variously called : old cul- 

 tures of tubercle bacilli mixed with 60 per cent, glycerine and 

 filtered through a Chamberlain-Pasteur filter, the filtrate thus 

 obtained being a dark-brown liquid, sp. gr. somewhat higher than 

 water, an odor like "beef extract," a sweetish taste, not soluble 

 in alcohol; according to Jollas, containing 50 per cent, water, 

 and showing a strong Biuret reaction ; he thinks it therefore a 

 toxalhumen. 1 milligramme of the lymph is supposed to contain 

 but ysnffo milligramme of the active principle. Dixon's lymph 

 is obtained in a very similar manner, and no doubt contains the 

 same principle. 



Dixon recommends instead of using the pure culture for 

 obtaining the lymph, the tuberculosis lung of calf, a portion of 

 which is treated with water and glycerine, and then filtered 

 through Chamberlain-Pasteur filter without pressure. 



Manner of Usiwj Koch's Lymph. One milligramme of the 



