294 Biological Chemistry. 



within a comparatively narrow range of temperature. The 

 investigation of the enzymes from the mammalian body 

 are usually carried out at the temperature of 3 7 '5 or 

 thereabouts, and for this purpose special chambers, which 

 can be maintained accurately at a constant temperature 

 ("incubators"), have been designed. At the temperature 

 of melting ice the action of the ferments of the mammalian 

 body are so intensely slow that they are almost negligible, 

 and the enzyme action can be almost stopped if the fer- 

 menting mixture is kept surrounded with ice. 



There are also well-defined limits of the reaction of 

 the medium within which a ferment will act. Thus pepsin 

 will digest proteins best in a medium which is fairly 

 strongly acid (N/20 hydrochloric acid), whereas the proteo- 

 clastic ferment of the pancreas will react in an alkaline 

 medium. Pepsin is inactive in an alkaline medium, 

 whereas trypsin, the pancreatic ferment, fails to act in an 

 acid medium. Invertase reacts best in a medium very 

 little removed from complete neutrality. A very slight 

 shifting of the reaction of the medium either to the acid 

 or the alkaline side from the point of optimal activity will 

 often appreciably affect its rate of action. The question of 

 the optimal conditions of reaction of the various ferments 

 has been the subject of repeated investigations in recent 

 years, and very fine physical methods must be employed 

 in order to obtain correct results. 



Finally, the action of the enzymes is often of an 

 intensely specific character. An excellent illustration of 

 this fact is afforded by the study of the enzymes which 

 bring about the hydrolysis of the two methyl glucosides. 

 It may be recalled that by the action of methyl alcohol on 

 glucose in the presence of hydrochloric acid two glucosides 

 have been obtained, to which the two following formulae 

 have been assigned : 



