10 INTRODUCTION 



sterilization measure the death of bacteria by their in- 

 ability to produce colonies, or to make a culture medium 

 cloudy. It has been frequently overlooked in the general 

 study of death that, to the bacteriologist, a cell is dead 

 when it is sterile, i.e., peymauently unable to reproduce. 

 Sooner or later such cells will also lose the other, more 

 conspicuous properties characteristic of life. Although, 

 with larger animals, sterility of the organism is not iden- 

 tical with death, any organism in which the individual 

 cells have lost the ability to multiply will sooner or later 

 lose the other, more conspicuous properties of life. 



The different criteria of death mentioned above refer 

 to the inactivation of different mechanisms which are 

 indispensable for the life and reproduction of the cell. 

 These mechanisms can be divided into five groups, ac- 

 cording to the functions they control: 



Group I : Mechanisms controlling the passage of 

 substances into and out of the cell; they are repre- 

 sented by the cell membrane. 



GroujD II : Mechanisms controlling the energy pro- 

 duction for all life activity ; they consist of enzymes. 



Group III : The synthesis mechanism which prob- 

 ably involves a large number of different catalysts 

 that control the synthesis of the cell constituents 

 from the food. 



Group IV : The multiplication mechanism : known 

 in higher organisms to have its seat in the nucleus. 



Group V : Mechanisms consisting of protein mole- 

 cules which often make up the bulk of the cytoplasm, 

 but are without definitely known physiological func- 

 tion, though they are essential for the life of the cell 

 since their denaturation causes death. (Such are 

 myosin, leguminin, glutinin, the globulins of bacte- 

 ria, etc.) 



