BACTERIAL PRODUCTS 4 1 



acid is first formed, and this is then converted into butyric- 

 acid : 



2C 3 H 6 3 = C 4 H 8 2 -V 2C0 2 + 2H 2 . 



The acetic acid fermentation. The conversion of alcohol 

 into acetic acid is also due to bacteria, familiar examples 

 of which are the souring of beer and wine. 



The reaction is : 



C 2 H 6 + 2 = CH 3 COOH + H 2 0. 



Citric, oxalic and other acid fermentations are also 

 known. 



Bacterial enzymes.- Many changes brought about by 

 bacteria and other micro-organisms are due to enzymes, 

 which may be not only mtra-cellular, but may escape from 

 the cells into the medium in which they are growing. 

 The most familiar examples are the peptonising enzymes 

 produced by bacteria which liquefy gelatin and digest 

 coagulated protein, fibrin, etc. The enzymes differ : an 

 organism which liquefies gelatin does not necessarily digest 

 blood-serum. The proteolytic enzyme is tryptic in nature 

 and escapes from the cells into the surrounding medium, 

 so that some of the liquefied gelatin free from cells or in 

 which their action is inhibited by an antiseptic, liquefies 

 other gelatin if added to it. Amylolytic enzymes are 

 also produced, such as amylase (digesting starch), maltase, 

 lactase, inulase, and invertase. Lipases and rennet-like 

 enzymes also occur. " Fermentation " of urea takes 

 place by means of an enzyme secreted by the Micrococcus 

 urece, and other organisms, with the formation of ammo- 

 nium carbonate. Some organisms are capable of digesting 

 cellulose and they may play a part in the digestive tract 

 of the herbivorous animals. These enzymes do not seem 

 to possess any poisonous action. 



Formation of pigment. Numerous organisms, especially 

 those of air and water, during their growth produce various 



