244 BIOLOGY OF SPECIALIZED GROUPS 



process. Progressive gangrene is also due in part to the 

 destruction of tissue by bacteria. 



Diseased conditions of this nature may also be produced in 

 the body by bacteria which cannot directly be called patho- 

 genic. 



(d) By the production of poisons or toxins by saprogenic 

 bacteria acting on food products outside the body. When 

 taken into the body through the digestive tract and absorbed, 

 these poisonous substances present give rise to serious in- 

 toxications. Similar morbid conditions may arise on account 

 of the action of saprogenic bacteria within the intestines. 

 The poisonous substances produced are called ptomains. 

 Meat poisoning, milk and ice cream poisoning, are examples 

 of diseased conditions arising from the action of ptomains. 



Occasionally, after parturition a portion of the placenta is 

 retained within the uterus, and it may be acted upon by 

 saprogenic bacteria. Ptomains generated and absorbed in 

 this region usually produce pronounced intoxications. 



Two principal factors are involved in the production of a dis- 

 ease by bacteria: (i) The entrance of bacteria into the 

 tissues of the body and their multiplication. This factor, it 

 will be recalled, constitutes infection. (2) The elaboration of 

 poisonous products by the bacteria which may act on the tis- 

 sues immediately surrounding them or on the entire body. 

 The latter factor constitutes what is known as poisoning or 

 intoxication. In most morbid conditions both of these factors 

 are concerned. In only a few cases is one factor alone involved. 



