38 PERMEABILITY OF ERYTHROCYTES. 



centration is determined for other salts, the isotonic solutions will 

 be established. Obviously the blood-plasma likewise is such an isotonic 

 solution, as the erythrocytes retain their form perfectly within it. 

 Those solutions are hyper isotonic, that is, of greater concentration, 

 that abstract water from the erythrocytes and therefore cause them to 

 shrink; while those solutions are designated hypisotonic, that is, of 

 feebler concentration, that yield up water to the erythrocytes and there- 

 fore cause them to swell. 



Although the erythrocytes preserve their form in isotonic solutions, 

 nevertheless an interchange may take place between the soluble sub- 

 stances in their interior and those of the surrounding fluid. Thus, 

 chlorids, phosphates, and proteids, for instance, pass from one to the 

 other. Under such circumstances, however, the isotonia is preserved. 

 If, therefore, substances pass from the erythrocytes into the surrounding 

 blood-plasma, other substances must, conversely, pass into them in 

 order to preserve the isotonia. The red corpuscles thus possess the 

 property of maintaining a constant degree of osmotic tension with refer- 

 ence to certain substances. If, for instance, small amounts of an acid, 

 and also carbon dioxid, be added to blood, albumin and phosphates 

 pass from the corpuscles into the plasma, while, conversely, chlorids 

 pass from the latter into the erythrocytes to maintain the isotonia. In 

 consequence, the corpuscles become somewhat globular and their diam- 

 eter diminishes in size. The blood-corpuscles exhibit the reverse inter- 

 change and effect in shape after addition of small amounts of alkali. 



Van 't Hoff discovered in 1887 the law that the interchange of sub- 

 stances in solution takes place according to the same laws as those 

 applicable to gases, namely, the osmotic pressure corresponds entirely 

 to the tension of a gas. The laws of gases laid down by Boyle- 

 Mariotte are, therefore, applicable also to substances in solution. Ac- 

 cordingly, and by reason of the diversity of the soluble substances con- 

 tained within the cells and in the surrounding fluids currents must arise 

 between the two in consequence of the osmotic pressure. If, therefore, 

 erythrocytes, which behave like sacs filled with saline solutions, are 

 placed in another saline solution, phenomena appear entirely analogous 

 to those that occur when a sac filled with gas is introduced into another 

 gas. 



The erythrocytes floating in a solution retain their volume only if the 

 fluid is isotonic; that is, if it exerts the same osmotic pressure and if 

 the substances dissolved in the surrounding solution cannot enter the 

 corpuscles. If the osmotic pressure in the surrounding fluid is dimin- 

 ished the corpuscle swells until it becomes completely dissolved in 

 water, whose osmotic pressure is zero. The blood then becomes lake- 

 colored. Exactly the same effect as is produced by distilled water 

 must be produced also by the solution of a substance, quite independ- 

 ently of the degree of its osmotic pressure, if the substance in solution 

 readily penetrates the blood-corpuscles, and therefore can exert no 

 pressure upon its wall. Under such circumstances also the corpuscle 

 will undergo dissolution and the blood become lake-colored. 



The phenomenon of the blood becoming lake-colored, which is easily 

 recognizable, indicates, therefore, that the blood-corpuscles are either 

 in a solution of low osmotic pressure or in a solution whose osmotic 

 pressure is not manifest because the wall of the corpuscles is impervious 



