22 BACTERIOLOGY 



the production of acetic acid in the manufacture of 

 vinegar. Others still produce gases and odors, some 

 fragrant, others foul and noxious, as in the putrefactive 

 processes. 



Poisons. Just as certain plants of the higher orders, 

 such as nux vomica, nightshade, and others, produce 

 substances which are poisonous to animal organisms, 

 so do these lower plant forms of bacteria produce poisons 

 which in many instances closely resemble the poisonous 

 alkaloids of the higher orders of plants. 



Ptomains. Certain of the complex alkaloidal poisons 

 produced by saprophytic bacteria in their growth on 

 dead organic matter are called ptomains. The ingestion 

 of food containing these poisons may result in illness or 

 even death. 



This is doubtless the only exception to the rule that 

 saprophytes are benefactors of mankind. In their zeal 

 to rid the earth of organic matter saprophytic germs 

 often attack food-stuffs which man has not yet aban- 

 doned. Upon the ingestion of meat, shell-fish, eggs, 

 milk, and other foods wherein such bacterial activity 

 has taken place ptomain-poisoning results. 



Toxins. The products of parasitic bacteria are 

 termed toxins, and to these poisonous substances are 

 due most of the pernicious effects of bacterial activity 

 in the animal body. 



Nearly all the changes in the organs of an animal 

 caused by bacterial disease can be reproduced by injec- 



