﻿STUDIES IN PLAGUE IMMUNITY. 329 



and during the past year nearly 200 vaccinations have been performed. 

 The cultures with which I have worked have proven themselves to be 

 entirely safe for human beings 12S and I have observed no unfavorable 

 results in the inoculated. However, as emphasized in my previous com- 

 munication, vaccinations against plague should not be made in man 

 unless the investigator can guarantee the particular organism with which 

 he is working to be of sufficient attenuation to be no longer dangerous 

 for human beings. Strains of the bacilli which invariably no longer 

 kill guinea pigs of 250 grams weight upon subcutaneous inoculation in 

 amounts of one agar slant culture are probably safe in small amounts 

 for human beings. Owing to the great stability in virulence of the 

 plague bacillus under certain conditions, its use in vaccination is much 

 simplified. 



During the past year and a half I have been able to detect no change 

 either in virulence, toxicity, or immunizing power in the strains Avith 

 which I have performed my vaccinations in man and in animals. The 

 cultures apparently possess the same immunizing power to-day as they 

 did at the commencement of the experiments. However, it is very 

 probable that they could be further attenuated by the artificial means 

 previously described. 



Douglas and W. Bullock 120 (whose article on plague has just appeared 

 in Allbutt and Eolleston's System of Medicine as my article goes to press) 

 in commenting upon my work in vaccination against plague make the 

 following statement : 



Naturally very great care would be necessary in recommending a method like 

 this on a big scale in plague stricken communities, as from unforeseen circum- 

 stances the virulence might increase and plague be induced. 



As I have pointed out, there is no evidence to support this statement, 

 and my cultures which for nearly two years have been used at intervals 

 in human beings are as safe for use in man to-day as they were at the time 

 of my first inoculations. 



123 The accident in relation to some inoculations which recently occurred in 

 Bilibid Prison in Manila and about which a report will shortly be made, was not 

 due to these plague vaccinations. 



120 Allbutt and Rolleston: System of Medicine (1907), 2, part 2, 408. 



