OF VITAL PHENOMENA 9 



In fact, the blood plasma itself comes in contact with some of 

 the cells. 



The blood plasma contains amino acids, sugar and fats for the 

 nourishment of the cells. The neutral salts in the plasma main- 

 tain the proper viscosity of the emulsoids, especially those of the 

 plasma membranes of the cells. The carbonates, phosphates and 

 to a small extent the proteins maintain the nearly neutral reaction 

 of the plasma. The chief function of the serum albumin and 

 globulin is not known; these proteins increase the viscosity of 

 the blood and throw more work on the heart in maintaining the 

 circulation. They are probably. not absorbed by the cells because 

 they appear to be different from the cell proteins. They prob- 

 ably exert a protective action on the plasma membranes of the 

 cells and increase the solubility of certain substances, such as 

 uric acid, by 'holding them in colloidal solution. Many inter- 

 mediate products of metabolism and waste products are carried 

 from certain cells to certain others by the blood. The presence 

 of hormones in the blood, which stimulate certain organs to activ- 

 ity, seems to be established, but the chemistry of these substances, 

 with the exception of adrenalin, is unknown. The plasma also 

 contains the substances that form the fibrin of blood clots, and 

 many enzymes whose function is not very clear. 



The exchange between the cells and the fluid bathing them 

 is caused by diffusion of dissolved substances, but if this were 

 unlimited the dissolved substances of all of the cells would be 

 the same, which is not the case. Diffusion is fairly rapid through 

 water but decreases as the viscosity increases. The increase of 

 viscosity due to emulsoids does not appear to explain entirely 

 the limitation of the diffusion of some substances, and the prob- 

 lem has never quite been solved, though many models showing 

 how it might occur have been borrowed from pure chemistry. 

 Traube's membranes form one series of models. If a solution 

 of potassium ferrocyanide is brought in contact with a solution 

 of a copper salt, a film of copper ferrocyanide is formed at the 

 plane of contact of the two liquids. This film is easily permeable 

 to water but impermeable to potassium ferrocyanide, copper salts 

 and many other substances, such as sugar. The permeability 

 of this membrane may be increased by treating it with certain 

 solutions without destroying its mechanical continuity. During 



