CHAPTER VII. 



FERMENTATIONS AND THE ACTION OF 

 ENZ YMES ( Continued). 



i. Putrefaction and Decay. After the death of 

 animals or plants the materials of which their bodies 

 are composed soon begin to undergo decomposition 

 unless special precautions are taken to prevent it by 

 cooking or the application of antiseptics. 



A host of bacteria of many different kinds set up 

 fermentations in the proteins, carbohydrates, fats, and 

 other organic compounds present, and step by step all 

 these substances are broken down into bodies of simpler 

 constitution, some of which have a disgusting odour. 

 Changes go on in all the different classes of compounds, 

 and the whole process is of a very complicated character ; 

 it is found, however, that the foul odour is particularly 

 associated with peculiar decompositions taking place in 

 the nitrogenous compounds. To the fermentations of 

 proteins, which are accompanied by the evolution of 

 evil-smelling products, the term putrefaction is applied. 

 Changes of this kind not only occur in the organic 

 compounds forming the dead bodies of plants and 

 animals, but also in various products, such as cooked 

 flesh, tinned foods, cheese, milk, and in dung and other 

 materials containing proteins. Putrefaction is most 

 evident when access of air is partially or entirely pre- 

 vented, i.e. when the bacteria causing it are living under 



