﻿XVI. CONCLUSION. 



In recommending for man vaccination against plague with suitable 

 cultures I wish to emphasize the fact that the method is not infallible 

 and that very brilliant results may not always be obtained by it. In the 

 vaccination of large numbers of human beings, owing to individual varia- 

 tions in susceptibility to plague infection and natural resistance, just as 

 in the experiments described in monkeys, certainly all of the individuals 

 will not be protected against lethal infection by a single vaccination with 

 one agar culture, but a certain proportion of them may be immunized 

 by this method and an appreciable degree of immunity may be retained 

 for at least nine months. The population in a plague stricken district 

 may gradually be immunized against this disease by the employment of 

 vaccination. 



In plague, as in smallpox vaccinations, it may frequently be necessary 

 to repeat the vaccination and perhaps with a larger dose, in order to 

 secure a satisfactory immunity. 



As yet we know of no practical method for the detection of those cases 

 which would require a second plague vaccination to produce in them a 

 sufficient immunity to protect them from the natural manner of infection 

 of the disease. It is perhaps possible that by a careful study of the opsonic 

 index in man and animals both before and after vaccination and with sub- 

 sequent attempts to infect the animal in order to observe the degree of 

 immunization which has resulted, a standard may be obtained by means 

 of which Ave may be able to judge from the amount of the increase in the 

 index whether the individual has acquired a satisfactory immunity from 

 the first vaccination. 



Owing to the complexity of the experiments necessary for the determi- 

 nation of the phenomenon of the fixation of the complement in the 

 serum of the vaccinated, this method will probably never assume prac- 

 tical value for the determination in a large number of cases of the 

 degree of plague immunity acquired. 



Professor Kitasato in a recent address published in a previous number 

 of this Journal 130 made the statement that : 



Plague is not only objectionable to the people of a locality but it is an enemy 

 to mankind in general. All civilized nations must fight this common enemy. 

 I believe there should be an international conference to discuss a plan to collect 

 money and to organize an international army to combat and vanquish this 

 disease wherever it appears. Expeditions should be sent to the interior regions 



130 This Journal (1906), 1, 465. 

 330 



