Factor Controlling Cell Metabolism. 



587 



The first general conclusion which may be drawn from these considerations 

 is that the great surface development in the cell or the organism produces 

 conditions which markedly affect the action of ferments in vivo when compared 

 with their action in vitro. 



We may now consider in some detail in what way this surface development 

 exercises its effect with regard to the metabolism of the cell. We find then, 

 firstly, that different parts of the cell present different conditions for the 

 action of ferments. Surface tension is operative at the periphery of the cell, 

 at the interface between cell and the surrounding medium. There the con- 

 ditions for ferment action will differ from the conditions presented by the 

 interior of the cell. But even in the interior of the cell, conditions in the 

 protoplasm surrounding the nucleus, vacuoles, granules, etc., will differ from 

 those presented by the rest of the cytoplasm. We must then conclude that 

 ferment action will not proceed evenly throughout the cell. It may be retarded 

 or inhibited in one part of the cell, while it is proceeding actively in another. 

 Whether it can even be reversed as the result of surface tension is not yet 

 clear from the experimental evidence before us. In this connection reference 

 may be made to the work of Warburg, who has demonstrated that the 

 oxidative processes in the cell are dependent on the structural parts of the 

 cell and not on the fluid cell contents. 



We have hitherto assumed, for the sake of simplicity, that the surface 

 tension of protoplasm is constant. But we know that it is always changing 

 as the result of chemical processes leading to the formation or disappearance 

 of surface-active substances. In cells with free surfaces, such as unicellular 

 organisms for instance, these fluctuations in surface tension result in the 

 decrease or increase of surface : they become manifest in the form of 

 movement. Amoeboid movement and ciliary movement have long been 

 recognised as surface-tension effects. The existence of such changes in different 

 physiological conditions of a unicellular organism has also been demonstrated 

 recently by MacCallum, by a micro-chemical study of the distribution of 

 potassium salts within the cell. 



Similar changes must occur also in cells aggregated in cell masses or organs. 

 But here, where the surfaces are not free, and possibly less elastic, and where 

 the cell cannot extend or diminish its surface except to a limited extent, the 

 result is, not movement, but alterations in the concentration and composition 

 of the substances constituting the surface layer of the cell, and this leads to 

 further alterations of the cell metabolism. 



Thus surface tension conditions cell metabolism, and is, in turn, also con- 

 ditioned by the metabolism of the cell. Chemical changes within the cytoplasm 

 may lead to the formation or disappearance of surface-active substances 



vol. lxxxviii. — b. 2 z 



