QUESTIONS AND ANSWERS 343 



brought to the hyperimmune stage agai^, and so on until, from 

 repeated amputations, their tails become too short for subsequent 

 bleedings. 



What is meant by the simultaneous method of immunization against 

 hog cholera? 



The simultaneous method consists of the inoculation of a hog with 

 a protective dose of immune serum and 2 or 3 c.c. of virulent blood 

 at the same time. This method confers an immunity which will last 

 six months and possibly one year. But it is not a practicable method 

 for inexperienced therapeutists, because of the danger of the virus 

 being scattered. 



How is tetanus antitoxin obtained? Discuss its use. 



Antitetanic serum is obtained from a horse which has been re- 

 peatedly inoculated with gradually-increasing amounts of tetanus 

 toxin, obtained from artificial cultures. Extremely minute doses 

 of the toxin are given at first, but at the end of several months a 

 pint or more produces no ill-effect. When, by test on guinea-pigs, 

 the serum of the horse is of the desired potency, the animal is bled 

 from the jugular at intervals ; the serum is drawn ofiE and aseptically 

 preserved. 



The antitoxin is measured in units; a unit representing the 

 amount necessary to neutralize a given amount of toxin, as proven 

 on guinea-pigs. 



Tetanus antitoxin is a valuable prophylactic or immunizing 

 agent. It should be administered in cases of infected wounds when- 

 ever there is a suspicion that tetanus bacilli may be present. If 

 given before the symptoms of tetanus appear, 750 units seem to be 

 sufficient to immunize. This immunity lasts but a few weeks. 

 There is a great diversity of opinion regarding its value as a cura- 

 tive agent. If it is of any value in this connection, it should be 

 given early and in large doses. There is no definite dosage ; as much 

 as 5000, and even 30,000, units have been given with equally varying 

 results. 



Vaccine Therapy 



What is vaccine therapy? 



Vaccine therapy is a method of producing an active immunity by 

 the injection of bacteria, or the products of bacterial growth, directly 

 into the patient. The virulence of the bacteria is modified by heat 

 or otherwise. As a result of their injection, antitoxins are produced 

 in the body. This is in contradistinction to serum therapy, which 

 produces a passive immunity. (See above.) 



