THE PROTOPLASMATIC MEMBRANE 



sol. So the plasmatic membrane would in my 

 opinion consist of two phases. One, the lipoid 

 phase, is given by a fat emulsion, the other, the 

 hydroid phase, by the protein solution which forms 

 the greater part of hyaloplasm. 



The Theory of Osmosis, or the diffusion of dis- 

 solved substances through membranes, has under- 

 gone many changes. There was a time when it 

 was generally believed that the diosmosis of a 

 substance depended upon the size of the pores of the 

 membrane and the size of the molecules of the 

 dissolved substance. Diosmosis cannot take place 

 when the pores are too small to let the molecules 

 pass. The membrane was considered to act like a 

 sieve for the molecules. This hypothesis does not 

 explain why fatty substances cannot pass mem- 

 branes which have taken up water. All signs show 

 rather that solution affinities play the most 

 important part in diosmosis. The membrane is 

 always permeable for a certain substance, when 

 this substance is soluble in the material of the 

 membrane. Nernst demonstrated this view by a 

 clear experiment. Ether is soluble in water as 

 well as in benzene. Benzene is soluble in ether only, 

 and insoluble in water. When a quantity of ben- 

 zene and a quantity of ether are separated from 

 each other by a layer of water, it is to be expected 

 that the ether will go through the layer of water, 

 but not the benzene. A continuous stream of 

 ether will pass through the water, but no stream 

 45 



