134 PRINCIPLES OF GENERAL PHYSIOLOGY 



The rabbit alone of all the animals tested fails to come into the corresponding 

 place in the two series. 



It is evident that the constituent acted on by saponin is of a kind different 

 from that which gives way when distended by osmosis. 



Again, while most lipoid solvents do, as a matter of fact, cause haemolysis, the 

 absence of an effect on the part of pure olein, while a mere trace of an oleatc is 

 sufficient, shows that the solvent action exerted on the lipoids of the cell membrane 

 is not the chief factor. A surface tension and adsorption effect is rather suggested, 

 leading to modifications in the colloidal state of the membrane. 



Mines (1912, p. 226) has shown that red blood corpuscles behave to the 

 agglutinating action of trivalent ions as if coated with an emulsoid colloid. Now 

 a suspension of lecithin in water behaves rather as a suspensoid towards electrolytes 

 (Forges and Neubauer, 1907), being precipitated by bivalent ions in low concentra- 

 tions. These facts suggest that the composition of the cell membrane is rather 

 that of protein than of lecithin. 



According to Pascucci (1905, p. 551), the stroma, or colourless portion, of the 

 red blood corpuscles consists of protein, lecithin, cholesterol and a cerebrosidc. 

 The greater part of this stroma forms the outer membrane. Various reasons are 

 given for the belief that there is very little, if any, protoplasmic skeleton within 

 the corpuscle, the chief reason being the separation, in certain conditions, of the 

 whole of the haemoglobin in large crystals within the corpuscle, while nothing is 

 to be seen of any protoplasmic substance between the crystals. 



The same investigator made artificial membranes of lecithin and cholesterol 

 (p. 555) by impregnation of a fine silk tissue, tied over the end of a glass tube, 

 with the fnsed lipoid or mixture of the two. Such membranes were found to be 

 attacked by haemolytic agents, saponin, cobra venom and tetanus toxin, in a 

 similar way to blood corpuscles, becoming permeable to haemoglobin. Lecithin 

 was much more readily attacked than was cholesterol. Lipoid solvents attacked 

 both, as would be expected, but dilute sulphuric acid had no action. On the 

 other hand alkalies, both ammonium and sodium hydroxides, rendered them 

 permeable. In this latter respect they differed from the normal cell mem- 

 brane, which, as we have seen, is permeable to the former, impermeable to 

 the latter. 



The experiments of Garmus (1912) on the living skin glands of the frog lead 

 him to the conclusion that the penetration of dyes into the cells of these glands 

 has no relation to their solubility in lipoids, since some of those that obtain 

 entrance are insoluble in lipoids. Moreover, poisons like saponin, sodium fluoride 

 and ether, which attack lipoids, do not affect the vital staining of the gland cells. 

 It is possible, however, that secreting cells behave in a different way from the 

 majority of other kinds of cells. 



Peskind (1903, p. 420) comes to the conclusion, from experimental results which are not 

 very convincing, that a "nucleo-protein" forms a constituent of the cell membrane, in con- 

 junction with lipoids. 



In respect of the question as to the penetration of substances into cells on 

 account of their solubility in lipoids, a certain confusion is apt to be made in tin- 

 interpretation of the action of such lipoid-soluble substances. It appears to be 

 assumed sometimes that, if a particular substance, say chloroform, is more 

 soluble in the lipoid membrane than it is in a watery liquid, the result will be 

 that there is a greater concentration of the chloroform in the interior of the 

 cell than in the surrounding liquid. On the contrary, if the solution inside the 

 cell is the same as that outside, the concentration will be identical ; the fact 

 of greater solubility in the lipoid only means that the concentration in the cell 

 membrane itself is higher. The meaning of the " partition coefficient " is that 

 there is a particular ratio between the j concentration of a substance in two 

 phases, according to its relative solubility in them, so that, unless the interior 

 of the cell has the same sol vent power as the lipoid itself, the "partition coefficient" 

 applies to the membrane only and not to the cell as a whole. Whether the 

 concentration is higher in the cell protoplasm depends on the amount of lipoids 

 which this contains. When it is found, for example, that narcotics as a class 



