VACCINE-THERAPY 183 



cases of advanced tuberculosis, it is possible, among other 

 reasons, that the system may be in a state of immunity to the 

 proteins of the bacillus. 



Biological Test for Tuberculosis. 



Where one possesses the necessary licence, and when 

 the question of an extended period is of no moment before 

 an opinion is required, the experimental inoculation of the 

 morbid material into a susceptible subject offers the best 

 means of forming an accurate diagnosis. 



The guinea-pig, by reason of its size and susceptibility 

 to tuberculosis, is the animal usually chosen for such an 

 investigation. 



Method. — Three guinea-pigs are tested at the outset with 

 tuberculin to assiu-e their freedom from the disease. 



If milk is the medium which is being investigated, a 

 quantity should be milked from the diseased quarter and 

 discarded, after which about a pint should be collected, 

 with great care, into a sterile vessel, and poured into sterile 

 tubes and centrifugalized for half an hour at a speed of 

 2,500 to 3,000 revolutions per minute. 



At the end of this time a semi-solid layer of cream will 

 have collected on the top. Under this is a layer of separated 

 milk, thin and watery, and at the bottom a sediment con- 

 taining cells, debris, and bacteria. Remove the cream clot, 

 which looks like a plug, and with a sterile pipette with- 

 draw all the liquid from the tube, leaving only 1 or 2 c.c. 

 of the sediment. Triturate this sediment thoroughly and 

 add 10 c.c. of normal saline solution, and centrifugalize 

 again for from ten to fifteen minutes. The supernatant 

 fluid should now be pipetted off, and film specimens made 

 of the sediment in order to detect the bacilli. 



The cream should also be examined in a similar manner, 

 as bacilli are sometimes found in this medium. 



The experimental animals should now be inoculated with 

 about 1 c.c. of the sediment or cream, usually on the inner 



