igii] Alfred P. Lothrop 89 



action exercise a retarding influence. Some substances which 

 destroy the life of protoplasm have no material effect on the power 

 of enzymes showing that enzyme action is distinct from protoplas- 

 mic activity. 



Enzymes may be divided into two classes, intracellular and 

 extracellular. The extracellular enzymes act outside the cell in 

 which they are formed or after being transformed into active 

 enzymes from their zymogens; they may be called secretion 

 enzymes, e. g. ptyalin, pepsin and trypsin. The intracellular 

 enzymes, on the other hand, exert their action within the cell and 

 can as a rule be extracted only with great difficulty. They are 

 fixed, and even after the death of the cell are set free only very 

 gradiially if the tissue is kept intact. 



The view has been expressed " that enzymes are not chemical 

 individuals but that various kinds of bodies may have conferred 

 upon them properties which cause them to behave like enzymes, so 

 that we have to deal with properties rather than substances." Still 

 another theorist has proposed the idea that enzymes act as radio- 

 active bodies and that radiations are the cause of the chemical 

 activity of enzymes. 



There are very many diffen^nt kinds of intracellular enzymes. 

 Practically every group of enzymes has several intracellular rep- 

 resentatives. In fact enzymes are cellular in origin, a great 

 majority of the enzymes exercise their activity within cells, and 

 most of the essential intracellular chemical changes are the results 

 of activities in which enzymes are involved. 



Various methods have been employed for the Isolation of intra- 

 cellular enzymes, such as autolysis, mincing the tissues, grinding 

 with quartz sand and filtration under high pressure. These enzymes 

 can be extracted with saline Solution saturated with Chloroform 

 or ether. 



The Unit of living substance may be considered as consisting 

 of a nucleus with which numerous side chains are connected, in 

 most cases of a protein-like nature. These side chains are bound 

 up in different ways and with different degrees of firmness. With 

 kidney it has been shown that by changing the salinity of the per- 

 fusing fluid from i per cent. to 4 per cent. the disruption was 



