PROTECTIVE INOCULATIONS. 297 



The view of Pfeiffer, founded upon his experimental results, is 

 that the destruction of the living cholera spirilla, which quickly takes 

 place in the peritoneal cavity of the guinea-pig, when at the same 

 time a minute quantity of serum from an immune animal is intro- 

 duced, is not directly due to the bactericidal action of this serum, but 

 that in some way it gives rise to a specific bactericidal action in the 

 exudate which is found in the peritoneal cavity as a result of such in- 

 jections. His experiments also lead him to the conclusion that this 

 is accomplished quite independently of phagocytosis. 



The brief review of experimental researches relating to cholera 

 immunity which we have made shows that, while there is a general 

 agreement as to the possibility of producing immunity in susceptible 

 animals, there is considerable difference of opinion as to the true ex- 

 planation of this immunity. The supposition that it is due to an 

 antitoxin which has the power of neutralizing the toxic products of 

 the cholera spirillum does not receive any support from the most re- 

 cent investigations those of Pfeiffer and Issaeff which, on the con- 

 trary, seem to establish the fact that this immunity depends upon an 

 increased bactericidal activity of the blood serum of immune animals. 

 A very curious fact developed by the researches of the bacteriologists 

 last named is that 



"The cholera serum which in the peritoneal cavity of guinea-pigs acted 

 only upon the cholera bacteria, and behaved toward other vibrios exactly like 

 the serum of normal animals, in a test tube killed all four species of vibrios 

 with equal rapidity." 



Unfortunately the evidence relating to the value of protective in- 

 oculations in man, although supported by the evidence already re- 

 ferred to as regards the lower animals, is, to a considerable extent, 

 unsatisfactory, owing to the difficulty of applying scientific methods 

 to experiments of this kind. The evidence, however, is in favor of 

 the view that a certain degree of protection is afforded by the subcu- 

 taneous injection of cholera cultures. Such protective inoculations 

 could not be expected to confer an absolute immunity, inasmuch as 

 the immunity resulting from a single attack has only a relative value, 

 and is probably not of long duration. 



We quote from Shakespeare's "Eeport on Cholera in Europe and 

 India, 1890," the following paragraphs relating to immunity as a 

 result of an attack of cholera : 



"IMMUNITY AFTER AN ATTACK OF CHOLERA EXPERIENCES IN 



FRANCE, 1884. 



"The Academy of Medicine of Paris directed a circular letter of questions 

 concerning cholera to the physicians of the localities infected by that disease 



