Surface Tension as a Factor Controlling Cell Metabolism. 585 



relatively high, and the reverse process when the blood-sugar concentration 

 falls. But the differences in the concentration of the blood-sugar which 

 accompany these processes are too slight to be an adequate explanation in 

 themselves, especially if we compare them with the large difference of con- 

 centration necessary to effect the reversal of a ferment action in vitro. 

 Moreover, when the liver is removed from the body the formation of such a 

 large amount of sugar takes place that the hydrolysis of glycogen should be 

 inhibited if the concentration of the sugar was the main factor. Nevertheless 

 the glycogen under these conditions completely disappears. The dis- 

 appearance of glycogen from the liver in the living animal as the result of 

 I; sugar puncture " or under the influence of the thyroid hormone cannot be 

 satisfactorily explained on the ground of changes in concentrations of the 

 reacting substances. 



In order to explain the predominance in vivo of the synthetic power of 

 ferments which in vitro act almost entirely as hydrolytic agents, the assump- 

 tion has been made that in vivo the products of synthetic action by a ferment 

 are withdrawn, as they are formed, from the sphere of action, so that the 

 equilibrium is always being disturbed in favour of the synthetic process. If 

 we take the liver again as an example, we find that with the ferment acting 

 in vitro the equilibrium point lies near the point of complete hydrolysis. 

 That means that a very small amount of glycogen can be synthesised by the 

 ferment, even in vitro. But since the glycogen thus formed remains in 

 solution the reaction stops when once this point of equilibrium is reached. 

 In the cell the slight amount of glycogen synthesised by the ferment is 

 deposited in an insoluble form as it is formed. The equilibrium is thus 

 disturbed and another slight amount of glycogen is formed. In other cases 

 it is assumed that the product of synthesis is removed by diffusion or excretion 

 or carried away by the tissue fluids. 



]STow this consideration may account for the fact that ferments which show 

 only a slight synthetic power in vitro have a marked synthetic action in vivo^ 

 It is doubtful whether this explanation can be applied in every case. It 

 certainly does not explain the " adaptability " of the cell, the readiness with 

 which the cell metabolism responds to slight changes in the environment. It 

 does not explain, for instance, the ease with which the liver cell regulates its 

 glycogenic function in the one or other direction, why a difference of less than 

 - l per cent, in the concentration of the blood-sugar determines whether 

 synthesis or hydrolysis of glycogen is to take place, or why the " piquure " and 

 the thyroid hormone produce a " mobilisation " of glycogen. 



It is clear, therefore, that there are factors conditioning the actions of 

 ferments within the cell which do not come into play when we study the 



