50 THE ACTION OF THE LIVING CELL 



and Effront (1905) have drawn attention to the fact 

 that while many bacteria and yeast do not suffer self- 

 digestion in culture medium, autolysis becomes rapid 

 when such cells are transferred to either distilled 

 water or saline solutions. Obviously under such con- 

 ditions the microorganisms are deprived of adequate 

 nutriment and hence are placed in a position com- 

 parable in some respects to the tissues of a starving 

 animal. 



Since these early investigations, a very considerable 

 literature has accumulated concerning the nature of 

 autolysis. In general it has been found, in agreement 

 with the fact that tissue proteases are active only in 

 acid media that the addition of acid substances in- 

 creases the rate of autolysis of excised tissues, whereas 

 the converse is true of alkalis. Indeed if tissues are 

 made sufficiently alkaline, autolysis ceases. In the case 

 of mammalian tissue no evidence of autolysis either 

 in vivo or in vitro can be detected as long as the tissues 

 are held at a hydrogen ion concentration equal to or 

 less than that characteristic of the animal's blood. It 

 has long been known that excised tissues develop a 

 post mortem acidity; and potentiometric measure- 

 ments by Dernby (1918) and by Kochler, Seving- 

 haus and Bradley (1921) have shown the velocity of 

 this acid production to be extremely rapid. While the 

 mechanism by which injured or dying tissues produce 

 the acid is not known, it is nevertheless real, as various 

 workers have actually isolated lactic acid from such 

 tissues. As a consequence any pathological change 

 which causes an increase in the acidity of a cell will re- 

 sult in an autolytic process, and diffusible substances 

 are produced which diffuse out of the cells ; hence the 



