DIFFISIOX AM) OSMOSIS 29 



aic sluiwn vniic's witli (liflciciit cells; with red coiijusclcs. I'oi- example, 

 the osmotic pressure influences arc very marked, as shown by the 

 wrinkling or crenation of the corpuscles when they are placed in 

 fluitls of higher concentration than the blood plasma, and by their 

 swelling and disintegration with escape of the hemoglobin {hemoly- 

 sin) when they are put into distilled water or solutions of less con- 

 centration than the plasma. Other tissue cells seem to undergo more 

 or less alteration from changes in the osmotic pressure in the fluids 

 surrounding tiieni. The dift"usion membrane that surrounds the cell 

 is generally nut well defincul, and for most cells seems to be but a 

 surface condensation of the protoplasm, perhaps formed through the 

 effects of surface tension. It seems probable that this surface dif- 

 fusion membrane contains a large proportion of cell lipoids, i.e., 

 cholesterol and phospholipins (for the red corpuscles this is practically 

 certain); hence substances soluble in lipoids penetrate the cell read- 

 ily, while to many substances insoluble in lipoids the cell is nearly 

 or quite impermeable (Overton). Probably the wall of the animal 

 cell is not so nearly semipermeable as is that of the plant cell, for 

 nowhere in the animal bod}- do we get such turgor in the cells as 

 we see in plant tissues. Lacking a cellulose wall, animal cells could 

 not develop such an internal pressure without rupturing and such 

 a process of rupturing {plasmorrhexis, plasmoptysis) does not seem 

 to be a normal occurrence in animal tissues. We shall be most 

 nearly correct, probably, if we look upon the animal cell as possess- 

 ing a delicate diffusion membrane at its surface, through which water 

 passes more readil}^ than do most crj'stalloids, and through which 

 colloids pass almost not at all, but the exclusion of each of these types 

 of substances is merel}^ relative and not absolute. AVithin the cell, 

 also, the colloids probably exist as a more or less well-developed 

 emulsion, so that we have here a practically limitless amount of 

 surface formation all through the protoplasm; such a structure could 

 permit the endless number of reactions of a living cell to go on side 

 by side in the same cell. Stuches b}' G. L. Kite^^ seem to show that 

 all of the protoplasm has much the same relation to solutions as does 

 the external layer or cell membrane, for he found that if drops of 

 solutions which can penetrate a cell from outside be injected directly 

 into a cell they diffuse through it, but substances which cannot pene- 

 trate from outside are also unable to diffuse through the cell after they 

 have been injected into it. 



Since osmotic pressure, exactly like gas pressure, is presumably 

 produced by the bombarding of the w^alls of the container by parti- 

 cles in the solution, the amount of pressure will vary in proportion 

 to the number of particles present. With non-electroh^es, such 

 as sugar and urea, the moving particles seem to be mole- 

 cules, and so a solution of sugar or urea will produce an osmotic 



's Amer. Jour. Physiol., 1915 (37), 282. 



