VACCINES. 



By L. Roger," 



Professor On the Faculty of Medicine, Umversitij of Paris, Member of the 



Academy of Medicine. 



The majority of infectious diseases do not occur a second time; 

 the first attack confers immimity. About a thousand years before 

 the Christian era this fact was known to the Chinese, among whom 

 smallpox made terrible ravages at that time. But all who survived 

 a first attack could live without inconvenience in infected places, so 

 that there was a considerable economic advantage in encouraging the 

 development of the disease during youth. In case the individual 

 died the loss to society was small ; in case of survival, the value of 

 that individual immune to a second attack was considerably in- 

 creased. Such were the reasons given by the Chinese for practising 

 variolation, or inoculation with the disease. It is remarkable that 

 such an idea should spring up and develop at a time when diseases 

 were more often attributed to divine wrath than to contagion, and 

 that it should lead to a prophylactic method which was not taken 

 up again until the end of the eighteenth century. 



Variolation was practised by inserting under the skin or in the 

 nostrils of subjects scabs taken from convalescents. This infection 

 through inoculation is much milder than infection contracted spon- 

 taneously. This result is easily explained : The pathogenic agent is 

 introduced into regions unfavorable for its development and with a 

 subject in good health, not predisposed to infection, while under 

 ordinary conditions of spontaneous infection it is more often the 

 case that resistance has been lowered through the agency of pre- 

 disposing or adjuvant causes. 



However, variolation is not always harmless ; the organism inocu- 

 lated may be in such a condition of predisposition that infection 

 spreads and takes a serious course, resulting sometimes in death. 

 And even if the inoculated subject resists it, the few pustules which 

 develop are capable of spreading the disease and constitute a danger 



1 Translated by permission from La Nature, Jan. 80, 1915. 



2 The frequency of Infections in time of war creating special interest in a study of their 

 prophylaxis, it has seemed to me useful to publish a brief general summary of the whole 

 subject. ^gg 



