CHEMICAL COMPOSITION OF THE HUMAN BODY 41 



ferments is unknown, but they have some properties in 

 common with proteids. They are soluble in water and 

 glycerin, are precipitated and partly coagulated by alcohol, 

 can be precipitated by salts, are not dialyzable, and give the 

 proteid color reactions. They are products of cellular 

 activity. 



The unformed ferments here referred to are to be distinguished 

 from the formed ferments which are organisms (bacteria, fungi,) 

 which, by contact t split up, certain substances (e.g. yeast, bac- 

 terium lactis. See page 20). 



Their most important property is that, in very small quan- 

 tities, they can chemically change unlimited quantities of 

 certain substances, without suffering any chemical change 

 themselves. Their action, in general, consists in a hydro- 

 lytic splitting up of the large molecule into smaller mole- 

 cules and in transforming the chemical potential energy into 

 kinetic energy. Their action depends upon the reaction and 

 concentration of the solution of the substances upon which 

 they act. The more concentrated the solutions, the less 

 active are the ferments. They are rendered inactive by 

 heating. 



Ferments are classified as: 



1. Coagulative ferments, which split up certain soluble proteids 

 into an insoluble and soluble part (e.g. the coagulative ferment 

 of blood, rennin of the stomach, myosin ferment). 



2. Digestive ferments, which, by hydrolytic splitting up, change 

 the insoluble or soluble proteid of food not capable of absorption 

 into a soluble form capable of absorption. These include: 



(a) Diastatic ferment (in saliva and pancreatic juice), which 

 changes starch to sugar. 



(b) Proteolytic ferment (in gastric and pancreatic juices), which 

 changes simple proteids to proteoses. 



(c) Stereolytic ferment (in pancreatic juice) which split neutral 

 fats into fatty acids and glycerin. 



Concerning the action of these ferments in detail, consult the 

 proper section in special physiology. 



