INTRODUCTION 



HISTORICAL AXD DEVELOPMENTAL. 



The conception of the nature of immunity Early Times 

 which was current at one period or another of 

 history had some relationship to the conception 

 of the etiology of diseases at those times. It will 

 be remembered that at one time diseases were 

 supposed to be imposed by an angry deity, and to 

 avert them various mysticisms were resorted to, 

 such as the utterance of incantations and the 

 wearing of talismans. On the other hand, a more 

 logical attempt to explain the natural immunity 

 of the Psylli against snake poison was made by 

 Pliny, who suggested that it might be due to their 

 habit of drinking water from wells in which pois- 

 onous snakes dwelt. This is not unlike our pres- 

 ent conception of active immunization. 



Von Behring quotes, literature to show that 

 among some primitive races of to-day, artificial 

 immunization is carried on; a Mozambique tribe 

 is said to inoculate against snake poison by rub- 

 bing into a small cutaneous incision a paste which 

 contains venom. Probably non-fatal quantities 

 are introduced in this way, resulting in the forma- 

 tion of venom antitoxin, a method comparable to 

 that used in the production of diphtheria anti- 

 toxin. 



At a very early period the possibility of habitua- 

 tion to poisonous drugs was recognized. We learn 

 that Mithridates by taking gradually increasing 

 closes of poisons established in himself resistance 



