INFECTION AND IMMUNITY. 



of this sort. It is stated also that he fed ducks 

 with poisons and then proposed to use their blood 

 as an antidote (serum therapy). The importance 

 of antidotes in the minds of the ancients may be 

 appreciated from the fact that epidemic diseases, 

 such as plague, cholera and smallpox, were at one 

 time considered as due to unknown poisons, which 

 might be comparable in nature to some known 

 poisons, as aconite. Mercury for syphilis, quinin 

 for malaria, and salicylic acid fcfr rheumatism 

 would certainly have fallen into the category of 

 antidotes,, and mercury may have been so con- 

 sidered. 



A historic illustration of the treatment of dis- 

 ease on a supposed etiologic basis is found in a 

 theory which was prevalent in the seventeenth 

 century, according to which diseases were either 

 acid or basic in character, and hence should be 

 treated, the one with an alkali, the other with an 

 acid. Sylvius considered plague to be of acid 

 nature and administered alkalies, while Etmliller 

 took the opposite view. 



Manifestly, rational treatment and prophylaxis 

 of the infectious diseases could not be undertaken 

 until their etiology was correctly understood. Yet 

 here, as so often happens in medicine, empiricism 

 preceded rationalism. For example, protective 

 inoculation did not become a principle until the 

 time of Pasteur, yet it had been practiced against 

 smallpox for centuries, and the method put on 

 its present basis by Jenner long before there was 

 any idea as to the principles involved in the pro- 

 tection. 

 Micro- The belief that invisible "animalcules" are able 



orii'si ii i.suis. . . . i i 



to cause morbid processes in man is a very old 



