THE BLOOD. 157 



blood being diluted ten times with a saline solution similar to that used 

 for red corpuscles, but containing a little methylene blue to stain the 

 leucocytes. 



THE RED BLOOD CORPUSCLES. 



Each red corpuscle is soft, and alters its shape readily so that it 

 can pass through even the narrowest capillary vessels. It is also 

 elastic, and readily regains its shape when the compressing influence is 

 removed. Two views are held as to the intimate structure of the 

 erythrocyte. According to one, the corpuscle consists of a sponge-like 

 framework (stroma) containing haemoglobin, the blood pigment, loosely 

 combined with the stroma. Schafer's view, on the other hand, is that 

 the corpuscle consists of an envelope containing the haemoglobin in 

 solution in its interior. Whichever view be adopted, it is clear, from 

 the behaviour of the corpuscle in presence of reagents, that its super- 

 ficial layer behaves to some extent as a semi-permeable membrane 

 readily allowing the passage of water but not of salts. Thus, if red 

 blood cells are placed in a fluid the salt content of which is markedly 

 below that of blood plasma, water passes into the corpuscle and 

 distends it, so that ultimately the membrane ruptures and the haemo- 

 globin is discharged. On the other hand, if the surrounding fluid is 

 hypertonic, for example 2 per cent. XaCl, water passes out of the 

 corpuscle, which becomes shrunken and creriated in consequence. In 

 9 per cent. NaCl, which is isotonic with mammalian blood plasma, the 

 cell is unaltered. 



The envelope of the corpuscle is dissolved by weak alkalies or by 

 ether, and this makes it probable that it is of a fatty nature. Bile 

 salts (which are solvents of fats), amyl alcohol, soaps, higher fatty 

 acids, and saponin or sapotoxin also dissolve the red corpuscles, setting 

 free the haemoglobin. The same result can be attained physically by 

 alternate freezing and thawing. The setting free of the haemoglobin 

 by any of these means is called haemolysis. 



Certain physiological substances also bring about haemolysis and 

 have been termed haemolysins. Snake venom, and frequently the serum 

 from an animal of another species, act in this way. Moreover, the 

 serum of an animal A, which is not naturally haemolytic for the blood 

 of another animal B, may be made haemolytic for the blood of that 

 animal, if A has been inoculated with blood from the species B some 

 days before the experiment is made. Thus rabbit's red corpuscles are 

 not broken up by the serum of a guinea-pig. If, however, rabbit's 

 blood has been previously injected into a guinea-pig, the serum from 

 the latter becomes haemolytic for rabbit's red corpuscles. 



