168 PHYSIOLOGY 



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

 being simply to hasten the attainment of the equilibrium 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 appear- 

 ance 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 obtained with distinctness only 

 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 interpreted 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, addrtion 

 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 which- 

 ever 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. 



