118 life's beginning on the earth 



A great deal of experimentation has been carried out in 

 numerous research laboratories in order to determine the 

 make-up of the thin envelope (semi-permeable membrane) 

 of the red blood cell. A chemical analysis is impossible 

 since the envelope is so extremely thin that it is hardly 

 visible. Only indirectly has some information about its 

 character been obtained, by determining the kind of mate- 

 rial which will penetrate it. To do this we observe whether 

 or not the blood cells break up in various solutions. We 

 have already seen that in a 1% salt solution the cell does 

 not break up, owing to the counterbalancing of the internal 

 pressure of the salt. This shows that the salt does not 

 penetrate. But if we place blood cells in a mixture of al- 

 cohol and water, they break up and we know then that the 

 alcohol penetrates into the cell. Alcohol lacks that essen- 

 tial property, non-penetration, which is indispensable for 

 osmotic pressure. The pressure inside the cells is not 

 counterbalanced and so they burst. 



Similar tests can be performed with a variety of sub- 

 stances. Ultimately we find that penetrating substances 

 are mostly those which dissolve in fat or oil, and since solu- 

 bility of the membrane obviously facilitates penetration, 

 we conclude that the cell membrane is some sort of fatty 

 material. Further experiments, however, show that fat 

 solubility is not the only condition required for penetration. 



Many problems concerning the nature of this film remain 

 unsettled, but science is on the way. The discovery of 

 osmotic pressure has established a working method which 

 may be used for thousands of experiments enabling us to 

 penetrate further and further into the secrets of the make-up 

 and functioning of the more complicated living organisms 

 which have evolved during millions of years, from enzy- 

 matic reactions in the ocean. 



The fundamental knowledge of the role of salt and water 

 is of practical importance in medicine and surgery. For 



