328 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 14 



the lipoids and cholesterin. This is the more probable as lecithin 

 and cholesterin have but slight surface tension effect and would 

 therefore tend to accumulate at surfaces. ^^ Indeed it is probable 

 that all substances that lower surface tension must tend to accumu- 

 late at surfaces and take part, to a greater or lesser degree, in the for- 

 mation of such membranes whether such substances come from 

 within the cell or from the liquids that bathe the cell. 



This hypothesis of the semi-permeability and lipoid character of 

 the cell-membrane has not been accepted universally. Czapek,^^ for 

 example, believes that the ability of substances to pass through the 

 cell-membrane is a function of their ability to affect surface tension 

 rather than a function of their oil solubility. However, substances 

 that lower surface tension seem also to be oil-soluble. Perhaps the 

 two traits are but expressions of the same underlying physical property. 

 Shryver^° believes the semi-permeability to be dependent upon the 

 presence of a gel in the membrane. However, all the theories explain- 

 ing the semi-permeability of cell-membranes that have been advanced 

 of recent years are based upon physical or physico-chemical consider- 

 ations. Not one assumes any dependence upon molecular structure 

 or chemical reaction. That is the important point for us this evening. 



We see then that the factors that determine the power of substances 

 to enter cells are physical properties rather than molecular structure 

 or chemical reactivity. If we examine the action substances exhibit 

 after they have obtained entrance into cells, we find that an immense 

 number of substances cg-use narcosis. In the lower organisms proto- 

 plasmic streaming and other forms of motion cease. In the higher 

 organisms endowed with a nervous system, this undergoes a more or 

 less complete paralysis. The most diverse substances have this 

 effect: — Pentane, chloroform, ether, alcohol, phenanthrene, salicylamid 

 monacetin. They have no common chemical properties except that 

 they are neither acids nor bases. They are spoken of as the "indiffer- 

 ent narcotics" to distinguish them from the narcotic alkaloids which 

 are bases. We have here again a common physiological action de- 



^8 It should, however, be noted that many food substances, for example glucose, cause 

 plasmolysis; yet they must enter cells for otherwise they could not nourish them. There 

 are undoubtedly other factors that enter into the structure of cell-membranes and a number 

 of theories on the subject have been advanced. 



" F. CzAPEK. Ueber die Oberfldchen-spannung mid den Lipoidgehalt der Plasmahaut 

 in den lebenden Pflanzenzellen. Ber. deutsch. botan. Ges. 28: 480. 1910. 



2° S. B. Shryver. Investigations dealing with the phenomena of "clot" formations, Part II. 

 Proc. Roy. Soc. B 87: 366. 1914. 



