170 GENERAL BIOLOGY OF MICRO-ORGANISMS 



nature of the reactions involved and to suggest the variety of 

 products which may arise from the decomposition of complex 

 organic substances. Some of these fermentative changes take 

 place to a large extent inside the microbic cell. Such is the 

 case in the alcoholic fermentation produced by saccharomyces. 

 The sugar-splitting or glycolytic ferments are found in the 

 cultures of many bacteria and molds. Less common are the 

 diastatic ferments capable of changing starch to dextrose, the 

 inverting ferments which change saccharose and lactose into 

 glucose and other hexoses, and the acetic ferments capable of 

 causing the oxidation of alcohol to produce vinegar. 



The fermentation or decomposition of proteins usually gives 

 rise to evil-swelling gases. This decomposition is called putrefac- 

 tion, and the organisms which cause it are called saprogenic or 

 putrefactive organisms. The nature of the products is much 

 influenced by the amount of oxygen available and the foulest 

 gases are produced especially in the absence of oxygen. Proteo- 

 lytic ferments of the same general nature as trypsin are produced 

 by many microbes. A few form rennet-like enzymes. Proteo- 

 lytic ferments which act in the presence of acid, like pepsin, are 

 produced by some molds and by some bacterial species. 



The decomposition of the complex protein molecules gives rise 

 to an enormous variety of intermediate products before the ulti- 

 mate analysis into ammonia, carbon dioxide, water, sulphates and 

 phosphates is accomplished. Many of these intermediate prod- 

 ucts are very unstable and of unknown chemical composition. 

 Some of them are highly poisonous. Brieger and his followers 

 were able to separate a number of the complex substituted ammo- 

 nia and ammonium compounds in a pure state and these par- 

 ticular bodies are known as putrefactive alkaloids, or as ptomains. 

 A simple ptomain is trimethylamin, N(CH 3 ) 3 ; a more complex 

 one cadaverin, HgN-CHa'CHa-CHa'CHa'CHa-NHa. Some of the 

 ptomains are poisonous. These various decomposition products 

 are for the most part secondary products resulting from the action 

 of enzymes upon the decomposing material. Many of them are 



