GENERAL PROPERTIES: THE CORPUSCLES. 423 



salts, and soaps, probably effect their action by their power of 

 uniting with the lipoid elements (lecithin, cholesterin) in the 

 stroma of the corpuscles. The framework of the corpuscles is 

 thus altered so that the hemoglobin is set free. The action of the 

 hemolysins and of agents which lower the osmotic pressure of the 

 plasma demands a more detailed description, as processes of great 

 practical importance are involved in these changes. 



Hemolysis Caused by Lowering the Osmotic Pressure of the Plasma. 

 The blood corpuscles contain a certain amount of water ( 57 to 

 64 per cent.), an amount insufficient to discharge the hemoglobin. 

 We may imagine that the osmotic pressure within the corpuscle is 

 such, compared with the osmotic pressure exerted by the salts in 

 the plasma, that a water equilibrium is established, and that, 

 although water molecules diffuse into and out of the corpuscle, 

 the exchange is equal in the two directions. If, however, the 

 outside plasma is diluted by the addition of water to any consider- 

 able extent, then the osmotic pressure outside the corpuscles is 

 correspondingly reduced, while that within the corpuscles is 

 unchanged. Consequently an increased amount of water will 

 pass into the corpuscles, sufficient, in fact, to mpture the cor- 

 puscles and thus discharge the hemoglobin. It is evident, 

 therefore, that in injecting liquids into the circulation or in 

 diluting blood outside the body care must be taken not to use 

 solutions whose osmotic pressure is markedly less than that of 

 blood-plasma, otherwise many of the red corpuscles may be 

 destroyed. Solutions whose osmotic pressure is the same as 

 that of the plasma are said to be isosmotic or isotonic with the 

 blood, those whose pressure is lower are designated as hypotonic, 

 and those whose pressure is higher as hypertonic.* The salt 

 that is contained in the plasma in largest amounts is sodium 

 chlorid. In mammalian serum it exists to an amount equal 

 to 0.56 per cent, and is probably responsible for the greater 

 part (60 per cent.) of the osmotic pressure shown by this liquid. 

 In making isotonic solutions this salt is, therefore, generally 

 employed. A solution containing nine-tenths of 1 per cent, of 

 sodium chlorid (NaCl, 0.9 per cent.) gives the same osmotic 

 pressure as plasma as determined by the effect of each on the 

 lowering of the freezing-point (see Appendix, Diffusion, Osmosis, 

 and Osmotic Pressure). Such a solution mixed with blood 

 should not and does not alter the water contents of the corpuscles. 

 One may, in fact, use a 0.7 per cent, solution of sodium chlorid 

 without causing any noticeable hemolysis, and this strength of 

 solution is frequently employed in infusions and experimental 



* For a full consideration of osmotic pressure in its relations to physio- 

 logical processes, see Hamburger, "Osmotischer Druck und lonenlehre " 

 Wiesbaden, 1902. 



