50 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



(&) Proteolytic — those which change proteids into proteoses and 

 peptones. Examples : pepsin, trypsin. 



(c) Steatolytic or lipolytic — those which split fats into fatty acids 

 and glycerin. An example, steapsin, is found in pancreatic juice. 



{d) Inversive— those which convert saccharoses (cane sugar, 

 maltose, lactose) into glucose. Examples : invertin of intestinal 

 juice and of yeast cells. 



(e) Coagulative — those which convert soluble into insoluble 

 proteids. Examples : rennet, fibrin ferment, myosin ferment. 



Most ferment actions are hydrolytic — i.e. water is added to the 

 material acted on, which then splits into new materials. This is seen 

 by the following examples : — 



1. Conversion of cellulose into carbonic acid and marsh gas 

 (methane) by putrefactive organisms. 



[cellulose] [water] [carbonic [methane] 



acid] 



2, Inversion of cane sugar by the unorganised ferment invertin : — • 



C,2H220n+H,0 = C6H,206+C6H,206 



[cane sugar] [water] [dextrose] [levulose] 



It appears also that some enzymes are oxygen carriers and 

 produce oxidation. They are termed oxidases. Very little is known 

 of these at present. 



A remarkable fact concerning the ferments is that the substances 

 they produce in time put a stop to their activity ; thus in the case 

 of the organised ferments the alcohol produced by yeast, the phenol, 

 cresol, &c., produced by putrefactive organisms from proteids, first 

 stop the growth of, and ultimately kill, the organisms which produce 

 them. In the case of the unorganised ferments, the products of their 

 activity hinder and finally stop their action, but on the removal of 

 these products the ferments resume work. 



This fact suggested to Croft Hill the question whether ferments 

 will act in the reverse manner to their usual action ; and in the 

 case of one ferment, at any rate, he found this to be the case. 

 Inverting ferments, as we have just seen, usually convert a 

 disaccharide into monosaccharides. One of these inverting 

 ferments, called maltase, coverts maltose into dextrose. If, 

 however, the ferment is allowed to act on strong solutions of 

 dextrose, it converts a small proportion of that sugar back into 

 maltose again. ' Keversible action ' has since this been shown to 

 occur in the case of other enzymes. 



Ferments act best at a temperature of about 40° C. Their 



