122 BACTERIOLOGY. 



change, are absolutely essential to the continued existence 

 of higher plants and animals. 



The products, elaborated by the majority of bacteria, 

 are practically harmless, if introduced into the living body. 

 It follows, therefore, that the vast majority of bacteria are 

 unable to produce poisoning, or disease, in man or in ani- 

 mals. A relatively small number of bacteria give rise to 

 poisonous products, and are also able to grow in the living 

 body. In such cases they live at the expense, and to the 

 injury of the host, and hence induce disease. Such organ- 

 isms are, therefore, designated as pathogenic. These will 

 receive special consideration in subsequent chapters. 

 There are bacteria which produce poisonous products, but 

 cannot grow in the living body. When such organisms de- 

 velop in foods they may give rise to poisonous products, 

 which will cause intoxication when the food is consumed. 

 The subject of poisonous foods is briefly touched upon in 

 Chapter XV'. 



The term toQ^icogevAc applies to all bacteria, which pro- 

 duce poison, irrespective as to whether they are able, or 

 unable, to grow in the living body. 



1 Additional information will be found in Vaughan and Novy, 

 Ptomains and Leucomai'ns, 3rd ed. 



