188 PHYSIOLOGY 



that the hydrolysis of esters by lipase is a reversible reaction, the 

 action of lipase being simply to hasten the attainment of the equili- 

 brium point between the four substances ester (or neutral fat), water, 

 fatty acid, and alcohol. Similar reversible effects have been described 

 for other ferments. Thus the addition of pepsin to a strong solution 

 of albumoses causes the appearance of an insoluble precipitate, which 

 is called plastein, and has been regarded as produced by the resynthesis 

 of the original protein molecule. 



If all ferment actions are in this way reversible, a possibility is 

 opened of regarding the synthetic processes occurring in the living 

 cell, as well as the processes of disintegration, as determined by the 

 action of enzymes. It must be noted that these effects are only 

 obtained with distinctness when dealing with concentrated solutions. 

 The degree of synthesis which would be produced in the very dilute 

 solutions of glucose, &c., occurring in the animal cell would therefore 

 be infinitesimal. But if a mechanism were provided for the immediate 

 separation of the synthetical product from the sphere of reaction, 

 either by removing it to a different part of the cell or by building it 

 up into some more complex body which was not acted on by the ferment, 

 the process of synthesis might go on indefinitely, and the infinitesimal 

 quantities be summated to an appreciable amount. 



Some experiments by Bertrand on fat synthesis have been inter- 

 preted as showing that the process of synthesis by ferments is not the 

 mere attainment of an equilibrium point in a reversible reaction. It 

 has long been known that watery extracts of the fresh pancreas split 

 neutral fats into the higher fatty acids and glycerine. This observer 

 has shown that if the pancreas be dried with alcohol and ether and 

 powdered, addition of the dry powder to a mixture of the higher fatty 

 acids and glycerine brings about a rapid synthesis of neutral fat. The 

 process of synthesis is at once stopped by the addition of water. In 

 this case either there are two ferments present, one a synthetising, the 

 other a hydrolysing, ferment, differing in their conditions of activity, 

 or there is one ferment which may act either as a fat-splitting or fat- 

 forming agent according to the conditions under which it is placed. 

 In the latter case the effect of the addition of water would be simply 

 to alter the equilibrium point of the mixture. It has been shown that 

 in all reversible reactions the equilibrium position is the same from 

 whichever side it be approached. The action of the ferment is to 

 hasten the attainment of equilibrium, the position of the latter being 

 determined by the relative concentration of the reacting molecules. 



