142 PRINCIPLES OF GENERAL PHYSIOLOGY 



evidence already referred to (page 107 above) indicates that they do not serve 

 for the nutrition of cells. It is certain, on the other hand, that the permeability 

 of the capillary wall may let through proteins, especially in pathological conditions. 

 In dropsy the continuous flow of lymph, which is obtained from a canula in the 

 subcutaneous tissue, contains protein and must have been filtered from the blood 

 capillaries. Direct evidence on the question at issue is, naturally, difficult to obtain. 



PHENOMENA DUE TO ACTION ON THE CELL MEMBRANE ITSELF 



There are many substances which exercise a powerful action on cell pro< 

 but which can be proved in certain cases not to enter the cell at all, and in 

 other cases, although they do enter the cell, they exercise no action after having 

 obtained entrance. 



One of these cases has been referred to in another connection, viz., the experi- 

 ments of O. Warburg (1910, p. 313) on the action of alkalies on the oxidation 

 processes in the developing egg of the sea urchin, in which it was found that the 

 consumption of oxygen could be doubled by the addition of very small amounts of 

 sodium hydroxide to the sea water in which the cells were immersed. Ammonium 

 hydroxide, on the other hand, produced scarcely any effect. By previously stain 

 ing the cells with neutral red, it could be shown that no sodium hydroxide entered 

 the cell ; whereas, if ammonium hydroxide was used, a rapid change of the dye to 

 yellow showed that the alkali had entered the cell. The action of alkali on 

 oxidation must, therefore, be exerted on the cell membrane itself. 



The following observations of the same experimenter (1911, p. 425) are of 

 interest in several ways. The young red blood corpuscles of the goose are 

 distinguished by considerable consumption of oxygen. This process, unlike that 

 of the sea urchin eggs, is not affected by salts. If, however, the cell membrane is 

 destroyed by careful freezing and thawing, which does not affect the total con- 

 sumption of oxygen, then the process becomes sensitive to salts, especially to 

 barium chloride. The unavoidable conclusion is, that, as long as the membrane is 

 intact, barium chloride cannot enter. In those cases in which it produces its 

 effect on the intact cell, it must do so by intermediation of the membrane, since 

 it cannot pass any further. 



Newton Harvey (1911, p. 546), working on Paramtecium, found that the 

 action of sodium hydroxide on the changes in behaviour, the formation of vesicles, 

 cessation of movement, and final death were all produced without the entrance of 

 the alkali into the cell substance. The same investigator later (1913), in a 

 special series of experiments, showed that the method used was free from 

 objection. 



The experiments of Bethe (1909) on Medusce showed that acids had an 

 accelerating action on their movements, although no change of dye indicator 

 within the cells occurred. 



An experiment of Overton's (1904, p. 202) shows'that the action of potassium 

 on muscle is also on the surface only. A sartorius muscle is transferred from 

 Ringer's solution, through 6 per cent, cane-sugar, to 2 per cent, potassium tartrate, 

 in which no change of weight takes place, showing that the cells are completely 

 impermeable to the salt, since the solution is isotonic with the cane-sugar. Never- 

 theless, the muscle is totally paralysed. On placing in Ringer's solution again, 

 the excitability is quickly regained. This latter fact confirms the view taken of 

 the action of tlie potassium salt as being on the cell membrane, since, if it had 

 penetrated into the interior, it is difficult to understand how it could pass out 

 again with such rapidity. 



Overton also showed (1902, 2), as will be remembered, that, if all the sodium 

 chloride be washed out of a muscle, it becomes inexcitable until more sodium 

 chloride is supplied. Now Fahr (1909) states that the only satisfactory 

 explanation of the results of his experiments is that the muscle cells themselves 

 normally contain no sodium at all. But since sodium is necessary for their activity, 

 it follows that it must act on the membrane, as this is the only part of the cell 

 with which it comes into relation. 





