192 STUDIES IN IMMUNITY. 



substance.* The same corpuscles, when mixed with either fresh 

 hemolytic serum or a mixture of fresh normal serum plus heated 

 hemolytic serum, are destroyed. Under these conditions it is easy 

 to demonstrate that they have fixed both the sensitizing substance 

 and the alexin. 



We may now consider what part of the corpuscles absorbs the 

 active substances. If corpuscles are placed in distilled water they 

 lose their hemoglobin, as we know, and are reduced to transparent 

 stromata floating in a red fluid. We may determine whether the 

 hemotoxic substances are fixed by the substances dissolved in the 

 laky fluid or by the stromata suspended in it. For such an experi- 

 ment the stromata are separated from the fluid in which they are 

 suspended. 



We take 3 c.c. of defibrinated rabbit blood, and preferably of blood 

 that has been washed in salt solution. To this is added 15 c.c. of 

 distilled water and a very red and nearly transparent fluid is ob- 

 tained. Microscopically the stromata are scarcely visible, are very 

 translucent, with a full round outline, and apparently are filled with 

 water. To this laked red fluid is added 1 c.c. of distilled water con- 

 taining 0.0975 of a gram of sodium chloride. The addition of this 

 salt solution restores the laked fluid to a tonicity corresponding to 

 normal salt solution. This addition of salt solution produces an 

 immediate clouding of the nearly transparent fluid. This cloud- 

 iness settles out in whitish flecks which gradually fall to the bottom 

 of the tube, leaving a clear supernatant fluid. Microscopical exam- 

 ination shows these flecks to be composed of agglutinated stromata. 

 These stromata have lost their very transparent and regularly 

 rounded form, have become more visible, and are flattened out into 

 thin concave disks. When seen in cross section they seem to have 

 undergone a veritable plasmolysis and it would seem as if the 

 stromata were simply inclosing membranes or veritable closed 

 sacs that swell in hypotonic fluids, and contract and flatten out in 

 more concentrated solutions. 



However that may be, the fluid is easily separable into two parts, 



either by deposition or, better, by centrifugalization : an upper part, 



which is absolutely limpid, with no microscopically visible elements; 



and the other reddish, opaque, and including large numbers of sus- 



* As we have already previously noted, they also fix the agglutinin. 



