114 THE FERMENTS. 



raents. Some of these, such as pepsin, can act to advantage only 

 in an acid medium ; while others, such as ptyalin, require an alka- 

 line reaction ; and still others can act in acid, alkaline, and neutral 

 media, but exhibit certain preferences. 



Generally speaking, the mode of action of the ferments is specific 

 /. ?., certain ferments will only act upon certain definite substances. 

 Fat-splitting ferments will only act upon fats, diastases only upon 

 carbohydrates, proteolytic ferments only upon albumins. This 

 specificity is in some instances very pronounced and is noticeable 

 even in individual members of a common group. The autolytic 

 ferments, for example, will not cause the cleavage of every albumin; 

 generally speaking those albumins which are foreign to the cell 

 which has furnished the particular ferment are attacked with greater 

 difficulty by the autolytic ferments of the cell. The autolytic 

 proteolytic ferment of the liver is thus incapable of hydrolyzing 

 the albumins of lung-tissue. For the lytic action of ferments of 

 one organ upon material which has originated in another organ 

 Jacoby has suggested the term heterolysis in contradistinction to 

 autolysis. 



It has long been known that the hydrolytic decomposition effected 

 by ferments is never carried to an end, and it is usually stated that 

 this is owing to the fact that a gradual increase in the production of 

 decomposition-products inhibits the action of the ferments in ques- 

 tion. In the light of more recent investigations, however, this 

 explanation is not satisfactory. It has been demonstrated that 

 maltase, when added to a solution of maltose, will cause inversion 

 of the latter to glucose. An end-reaction is then not obtained ; but 

 if this solution is now added to a solution of glucose in turn, at a 

 time when further inversion does not occur, it will be noted that a 

 retransformation of glucose to maltose takes place, which, however, 

 is likewise not complete. It thus appears that the ferment is not 

 only capable of causing the hydrolytic decomposition, but also the 

 synthesis of maltose ; but that in so doing its action ceases as soon 

 as a certain equilibrium of reaction has been established. This 

 reversible action on the part of ferments is, of course, of the greatest 

 interest to the physiological chemist, in showing that the complex 

 syntheses which take place both in plant and in animal life may, to 

 a certain extent at least, be referable to such action, and to forces 

 which are probably at work in the non-organized world. 



Croft Hill has shown that lactase is capable of synthetic action 

 with a concentrated solution of galactose and glucose. Very curi- 

 ously, however, in the use of the synthetic production of both mal- 

 tose and lactose, isomaltose and isolactose are formed, which the 

 corresponding ferments are not able to split. 



Kastle and Loevenhart have demonstrated the reversible action 

 of lipase in the case of ethyl butyrate. 



In the case of the proteolytic ferments similar conditions probably 



