Microhic Diseases Individually Considered. 235 



tubercles collected in a state of purity and reduced to 

 pulp — the inoculation can with advantage be made 

 into the peritoneal cavity, thus obtaining a more 

 rapid evolution ; when we have only at our disposal 

 virulent matters contaminated with other germs, such 

 as pus or nasal discharge, we must content ourselves 

 with subcutaneous inoculation. A region should be 

 preferred in which the lymph glands are easily ex- 

 plorable in order that the progress of the lesions may 

 be followed. In default of this exploration the ema- 

 ciation of the subject after the time specified above 

 will enable us to affirm, before the autopsy, that the 

 inoculation has been successful. 



Tiibercidin. — Another means of diagnosis consists in 

 testing with Koch's lymph or tuberculin. 



Cultures of the tubercle bacillus contain a soluble 

 product discovered by Koch which possesses a very 

 remarkable property. This substance is without efiect 

 on healthy individuals, whilst it is toxic for the tuber- 

 culous. The name tuberculin has been given to a 

 glycerin extract of cultures which contain this active 

 agent. Since his first discoveries Koch has simplified 

 the process by which it is prepared. Large cultures 

 in veal bouillon, to which has been added one per cent 

 of peptone and from four to five per cent of glycerin, 

 are reduced to one-tenth their volume at a tempera- 

 ture of about 100°, then filtered through porcelain so 

 as to remove all the microbes. The tuberculin thus 

 obtained contains enough glycerin for its own preser- 

 vation. The product has not a stable composition. 

 Koch recommends testing its activity on tuberculous 

 guinea pigs. According to this author, a good speci- 

 men of tuberculin, in the dose of one centigram, kills 



