550 LECTURE XXIII. 



enveloped with a substance similar to fat which forms a semi-permeable 

 wall. It is certain that the red blood-corpuscles, also called erythrocytes, 

 do not take up all substances. The wall will not allow many salts to pass 

 through, though it is easily penetrated by water. If the erythrocytes are 

 placed in a solution of common salt, whose osmotic pressure corresponds 

 exactly to that of blood-plasma, the blood-corpuscles will remain unchanged. 

 Such a salt solution is said to be isotonic. Its concentration is different 

 for different species of animals, and is called a "physiological salt solution." 

 In/tlie case of mammals such a solution contains 0.9 per cent of sodium 

 chloride. If there is more salt present in the solution, it is said to be 

 hyperisotonic, in which case the red corpuscles will give up water to 

 the solution and shrink in size. Conversely in a hypisotonic salt solution 

 (one containing less salt than an isotonic solution) the corpuscles take 

 up water and swell. This swelling may take place to such an extent 

 that the red corpuscles lose the characteristic pigment which passes 

 into solution. In this case the blood undergoes a peculiar transfor- 

 mation. Whereas it was opaque before, it now becomes a clear, trans- 

 parent, red-colored liquid. The blood is said to be "laked." l In the 

 laked blood, the blood-corpuscles robbed of their hemoglobin, the so-called 

 "shades," are found in which only stroma is present. The "shades" 

 appear under the microscope as colorless structures, often retaining the 

 form of the erythrocytes. The red corpuscles are not impenetrable to all 

 substances. Urea, for example, is taken up by the blood-disks. If urea 

 is added to blood it distributes itself equally between the blood-corpuscles 

 and the plasma. Its solutions, therefore, exert no osmotic pressure upon 

 the red corpuscles. The latter behave in urea solutions of all concentra- 

 tions exactly as in distilled water. They give up their hemoglobin to the 

 urea solution; this is not the case if the urea is added to an isotonic solution 

 of common salt. We know of certain substances, such as ammonium 

 chloride, for example, which behave differently from urea in the last case. 

 The wall surrounding the red corpuscles is readily penetrated by this salt, 

 and the hemoglobin goes into solution even if the ammonium chloride is 

 added to an isotonic common salt solution. Ammonium chloride, there- 

 fore, has a poisonous action upon the blood-corpuscles. A great many 

 experiments have been carried out with regard to the permeability of the 

 red corpuscles. At present they do not give us much information con- 

 cerning the behavior of the blood-corpuscles in the blood itself, and con- 

 cerning the substances dissolved in the plasma. We are not justified in 

 applying experiments performed under peculiar conditions to the blood 

 itself as it exists in the living organism. 



The exit of the pigment from the red corpuscles, a process which is 



1 Hans Koeppe: Pfluger's Arch. 103, 140 (1904); ibid. 107, 86, 183 (1905). 



