36 PHYSIOLOGY FOR DENTAL STUDENTS. 



interfered with by unfavorable conditions than those of extra- 

 cellular enzymes. This is because the former become inactive 

 whenever anything occurs to destroy the protoplasm of the cell 

 in which they act. The living protoplasm is necessary to bring 

 the substrat in contact with them. On this account enzymes used 

 to be classified into organized and unorganized. We know that 

 there really is no difference in the enzyme itself ; the only differ- 

 ence is with regard to the place of activity. The cells that com- 

 pose the tissues of animals perform their various chemical activi- 

 ties in virtue of the intracellular enzymes which they contain. 

 These are, therefore, the chemical reagents of the laboratory of 

 life. After the animal dies, the intracellular enzymes may go 

 on acting for a time and digest the cells from within. This is 

 called autolysis. 



Enzymes are classified into groups according to the nature of 

 the chemical action which they accelerate. Thus: 



Hydrolytic enzymes cause large molecules to take up water 

 and split into small molecules. (Most of the digestive 

 enzymes belong to this class.) 



Oxidative enzymes (oxydases) encourage oxidation. 



Deamidating remove NH 2 group. 



Coagulative convert soluble into insoluble proteins. 



Each group is further subdivided according to the nature of 

 the substrat on which the enzymes act ; e. g., hydrolytic enzymes 

 are subdivided into amylolases acting on starch; invertases 

 acting on disaccharides ; proteases acting on proteins; ureases 

 acting on urea, etc. 



When enzymes are repeatedly injected into the blood, or under 

 certain other conditions, they have the power, like toxines, of 

 producing antienzymcs. As their name signifies, these are bodies 

 which retard the action of enzymes. Thus, if some blood serum 

 from an animal into which trypsin has been injected for some 

 days previously be mixed with a trypsin solution, the mixture 

 will digest protein very slowly, if at all, when compared with a 

 mixture of the same amount of trypsiu and protein (see also 

 p. 78). 



