170 STUDIES IN IMMUNITY. 



This experiment may be done more exactly as follows: A normal guinea-pig 

 of 600 grams is given 3 c.c. of guinea-pig serum active against rabbit corpuscles. 

 A normal serum has been previously obtained from this guinea-pig before injec- 

 tion (serum A). Serum B is obtained by bleeding the guinea-pig 24 hours after 

 injection. A mixture is made of one part of active serum (the same as used for 

 injection) and nineteen parts of serum A (equals serum C). This mixture and 

 also serum B are then heated for half an hour to 55 degrees to destroy the alexin, 

 since the amount of alexin in these two fluids might differ. A comparison of the 

 power of sera B and C to form a dissolving mixture for rabbit corpuscles with 

 normal serum A containing alexin, may then be made. This is done by deter- 

 mining the smallest amount of B and of "C respectively, which, in the presence 

 of a given amount of serum A, will completely dissolve a given quantity of red 

 blood cells. B is found to be slightly less active than C. From the result we should 

 conclude that the active serum when injected subcutaneously in a guinea-pig of 

 600 grams is simply diluted in slightly more than 60 c.c. of body fluid. This 

 dilution corresponds pretty well to what actually takes place. 



The different facts considered up to this point, namely, concerning 

 the identity in action of the sera on corpuscles whether in vivo or 

 in vitro, lead us to the conclusion previously offered for antimicro- 

 bial sera. Antihematic sera have no particular cellulicidal sub- 

 stance; the cellulicidal substance (alexin) destroyed at 55 degrees 

 is present, not only in immunized animals, but also in normal animals. 

 Although it is only slightly active in normal serum it acts energeti- 

 cally in the serum of treated animals because it occurs there in con- 

 junction with the proper substance of this active serum which 

 resists heating to 55 degrees or 60 degrees and favors the action of 

 the alexin. The intense cellulicidal power which appears in the 

 serum of a normal animal following the injection of active serum 

 is not due to a reaction on the part of the animal nor to any trans- 

 formation of the substance injected, but simply to the encounter 

 within the animal body of the two substances that are necessary to form 

 intense cellulicidal power. The animal already contained one of 

 -the substances, the alexin, and the other, a specific substance 

 characteristic of active serum, is furnished by the injection. The 

 union of these two substances, which occurs in the animal body, 

 may also be produced in vitro by simply mixing normal serum with 

 either intact or previously heated active serum.* 



* We shall not consider at this point in all its details the conclusions that 

 we offered in 1895 concerning antimicrobial sera (see p. 79) applicable in this 

 instance to antihematic sera. 



