14 INTEOUUCTION. 



In the study of these we must not only ascertain the nature 

 of the poisons which they produce, but must know the con- 

 ditions under which they can multiply and elaborate these 

 poisons. To these points the following pages, in so far as 

 they treat of. the infectious diseases, will be devoted. 



However, all diseases are not infectious ; all poisons 

 formed within the body do not owe their existence to bac- 

 teria. Some originate in the altered metabolism of the 

 various tissues, and these will be discussed under the auto- 

 genous diseases. 



