OSMOTIC PRESSURE 



11 



fluids has been compared, the objects in view being to see whether 

 osmotic pressure is a property which changes under different physiological 

 and pathological conditions, and to find out by comparison of the osmotic 

 pressures of the fluids in contact with a membrane, whether physical 

 forces alone can be held responsible for the transference of substances 

 through it from one fluid to the other. 



THE ROLE OF OSMOSIS, DIFFUSION, AND ALLIED PROCESSES 

 IN PHYSIOLOGICAL MECHANISMS 



The Transference of Substances Through Cell Membranes. An ac- 

 count of some of the investigations in which the foregoing meth- 



Fig. 4. Apparatus for measurement of the depression of freezing point of solutions. The 

 solution is placed in the large test tube with the side arm, and in it is suspended the bulb 

 of a Beckmann thermometer with a platinum loop to serve for stirring. The upper end^of 

 the mercury column of the thermometer is shown magnified at the upper left corner. The 

 amount of mercury in the thermometer tube can be regulated by tapping the upper end with 

 the thermometer in various positions. The test tube is protected by an outer tube, which is 

 then placed in a vessel containing a freezing mixture. 



ods have been used will illustrate their value in revealing the mech- 

 anism involved in the transference of water and dissolved substances 

 through cell membranes, as occurs in absorption of food in the 

 intestine, in the formation of lymph and urine, and so forth. In em- 

 ploying physical methods in the elucidation of such problems, it is 

 always most necessary to proceed with great care, since the physical 



