386 BLOOD AND LYMPH. 



salts. (4) By adding amyl-alcohol. (5) By adding the serum 

 from the blood of certain animals. (6) By adding saponin or 

 sapo toxin. (7) By the addition of an excess of alkali. (8) 

 By various toxins found in snake venom or in the serum of other 

 animals or among the products of bacterial activity (natural 

 hemolysins) or by similar organic substances produced within the 

 body by the process of immunizing. Two of these methods de- 

 mand especial mention, as they involve the consideration of proc- 

 esses of great physiological importance. 



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 discharge and dissolve 

 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 

 hypo tonic, and those whose pressure is higher as hypertonic.* 

 The salt that is contained in the plasma in largest amounts is 

 sodium chlorid. In making isotonic solutions this salt is there- 

 fore 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 with- 

 out causing any noticeable hemolysis, and this strength of solution 

 is generally employed in infusions and experimental work; it con- 

 stitutes what is known in the laboratories as normal saline or physio- 



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

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

 Wiesbaden, 1902. 



