MODE OF ACTION OF CYTOLYTIC SERA. 239 



even after a prolonged contact (16 hours) normal guinea-pig 

 serum (3 c.c.) mixed with defibrinated, carefully washed rabbit 

 blood (6 c.c.) has lost all of its alexin for rabbit corpuscles. The 

 supernatant fluid from such a mixture after centrifugalization is 

 very red* and has no effect on freshly added rabbit corpuscles; in 

 other words, it has become inactive for these corpuscles; but it will 

 still produce a distinct hemolysis of hen corpuscles. 



We may be sure that this fluid still contains a definite amount 

 of alexin, to the presence of which is due the destruction of hen 

 corpuscles. As far as rabbit corpuscles are concerned, a state of 

 equilibrium in the division of the alexin has been established (and 

 in producing this state the products from destroyed rabbit cor- 

 puscles have perhaps contributed), and further attack on the same 

 corpuscles thereby prevented. 



This state of equilibrium is easily broken: it suffices to increase 

 by means of a sensitizer the avidity of the rabbit corpuscles for 

 alexin. The reddish fluid under consideration will still destroy 

 fresh rabbit corpuscles energetically if they are sensitized. In a 

 mixture of 0.2 of a cubic centimeter of red fluid, the same amount 

 of washed rabbit blood, and 0.6 of a cubic centimeter of heated 

 specific guinea-pig serum, hemolysis occurs rapidly and completely. 

 To render the experiment more complete another mixture is pre- 

 pared, containing, in the place of the sensitizing serum, 0.6 of a cubic 

 centimeter of heated normal guinea-pig serum (56 degrees). In 

 this mixture there is, of course, no destruction of the rabbit corpus- 

 cles. A few hours later 0.3 of a cubic centimeter of specific anti- 

 hen serum (56 degrees) plus 0.1 of a cubic centimeter of defibri- 

 nated washed hen blood is added to each tube. The hen corpuscles 

 are rapidly destroyed in the second tube, but remain quite intact in 

 the first. 



It is evident, then, that the normal alexic serum has by no means 

 been exhausted by the long contact with an excess of rabbit cor- 

 puscles, but has retained a considerable amount of the alexin fitted 

 to destroy these same corpuscles. If the rabbit corpuscles are 

 sensitized, the absorption of alexin takes place much more energeti- 

 cally, and new corpuscles of another species subsequently intro- 

 duced remain unchanged. 



* There are many intact rabbit corpuscles present in the sediment. 



