AGGLUTINATION AND DISSOLUTION. 167 



only on the protoplasm of the corpuscle and does not affect the 

 nucleus. 



A microscopical examination of a mixture of hen blood and 

 active serum shows that the red blood corpuscles are clumped in 

 more or less compact masses and reduced to their nuclei. Nothing 

 remains of the protoplasm but a very delicate stroma. On stain- 

 ing with eosin followed by methylene blue no protoplasmic out- 

 line is visible; the affinity of protoplasm for eosin has disappeared; 

 the nuclei, however, stain blue as usual. Such lesions of the 

 red blood corpuscles, however, are not characteristic of an active 

 specific serum alone, but may occur when hen corpuscles are 

 placed in contact with a sufficiently active normal serum, as for 

 example dog serum. The active serum is distinguished only by 

 the remarkable intensity of its properties against the corpuscles in 

 question. 



The destructive property is destroyed on heating the serum to 

 55 degrees, but may be restored by the addition of fresh normal 

 rabbit or guinea-pig serum to the heated serum. This fresh normal 

 serum contains, as we know, alexin.* The heated active serum re- 

 tains both its agglutinating property and the property of forming 

 with alexin a mixture that has intense hemolytic power. We shall 

 not insist further on the significance of these facts nor on the analo- 

 gies between antimicrobial sera and antihematic sera in this 

 respect, since they have already been pointed out in our preceding 

 article. 



If defibrinated hen blood, to which heated active serum has been 

 added, is introduced into the peritoneal cavity of a normal rabbit, 

 a rapid destruction of the protoplasm of the corpuscles may be 

 noted under the influence of the alexin from the peritoneal exudate. 

 The nuclei of the corpuscles, deprived of their protoplasm and 

 resisting the action of the body fluid in vivo as well as in vitro, are 

 found in such an exudate. These nuclei are later taken up by the 

 macrophages of the peritoneal cavity. 



The question arises as to whether an antihematic serum from a 

 treated animal will endow a normal animal of the same species with 

 a " passive immunity" analogous in its characteristics to that 



* The normal serum may be replaced by the peritoneal exudate from a normal 

 rabbit which also contains alexin. 



