138 STUDIES IN IMMUNITY. 



clump the red blood cells in fifteen parts of defibrinated rabbit 

 blood. 



Second : The corpuscles that have been clumped by this serum 

 subsequently undergo rapid and complete destruction; for example, 

 in a mixture of one part of defibrinated rabbit blood and two or 

 three parts of active serum the mixture becomes red and perfectly 

 transparent in 2 or 3 minutes. Microscopically, nothing but 

 the stromata of the corpuscles are found in the fluid; they appear 

 more or less distorted, very transparent, without their usual sheen, 

 and rather difficult to discern. 



Third : If this active guinea-pig serum is heated to 55 degrees for 

 half an hour it loses the property of destroying rabbit corpuscles, 

 but still agglutinates them. 



Fourth : if a certain quantity of fresh normal guinea-pig serum 

 is added to a mixture of defibrinated rabbit blood and specific serum 

 heated to 55 degrees, the phenomena of destruction reappear in 

 their entirety. The mixture becomes limpid and red in a few 

 minutes. It is rather surprising to find, moreover, that the experi- 

 ment succeeds perfectly if fresh serum from the very rabbit whose 

 corpuscles are affected is added to the mixture of corpuscles and 

 heated specific serum. That is to say, the corpuscles of this rabbit 

 have become susceptible to their own alexin under the influence 

 of the foreign clumping substance from a guinea-pig treated with 

 defibrinated rabbit blood. 



Fifth : Although it is true that active guinea-pig serum loses its 

 destructive property by heating to 55 degrees it is not quite exact 

 to say that defibrinated rabbit blood when mixed with such a 

 serum remains wholly intact. There is sufficient destruction of red 

 blood cells to give the fluid a more or less reddish color, although 

 the destruction is only partial and very slow. This destruction is 

 due to the fact that the defibrinated blood contains, not only 

 corpuscles, but also serums containing a certain amount of alexin, 

 and, as we have just seen, normal rabbit alexin will act on rabbit 

 corpuscles when the latter have been affected by the clumping sub- 

 stance of active serum. The amount of alexin in the defibrinated 

 rabbit blood, however, is not sufficient to destroy a large number 

 of corpuscles, which explains why the destruction of red blood cells 

 is very slow and only partial in such a mixture. 



