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 “Report 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 
