OSMOTIC PRESSURE 



11 



The depression of the freezing points produced by the various body 

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

 osmotic pressure is a property which changes under different physiologic 

 and pathologic 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 Physiologic 



Mechanisms 



An account of some of the investigations in which the foregoing 

 methods have been used will illustrate their value in revealing the 



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. 



mechanism involved in the transference of water and dissolved sub- 

 stances 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 



