328 STUDIES IN IMMUNITY. 



If it be true that the agglutination of barium sulphate and heated 

 serum depends on the diminution of the colloidal condition of the 

 latter, we should expect to obtain different phenomena, in accord- 

 ance with whether we add a large or small amount of heated serum 

 to a given amount of suspension. We put the same amount of 

 barium sulphate (4 drops) in two tubes and add to one 0.95 c.c. of 

 salt solution plus 0.05 c.c. of heated serum and to the other 0.6 c.c. 

 of salt solution plus 0.4 c.c. of the same serum. In the first tube, 

 containing a small amount of serum, a fine clumping occurs, but the 

 sulphate remains dissociated in the second tube. The loss of 

 dissociating property of the serum by heat may be made up for, 

 then, by adding a larger amount of the heated serum. 



Not only will a large dose of heated serum dissociate fresh barium 

 sulphate, but it will also restore to a fine suspension sulphate that 

 has been previously agglutinated by a small dose of serum. We 

 prepare two tubes containing each 0.95 of a cubic centimeter of 

 salt solution and 0.05 c.c. of heated serum and 4 drops of our 

 emulsion of sulphate-; when agglutination has become complete, to 

 one of the tubes we add 0.35 of a cubic centimeter of the same 

 heated serum and to the other the same amount of salt solution, 

 and shake. The agglutination persists in the second tube, but the 

 suspension becomes dissociated in the first tube; the first tube then 

 looks exactly as if 0.4 of a cubic centimeter of heated serum had 

 been added in a single dose to 4 drops of sulphate.* 



A large dose of heated diluted serum is necessary to dissociate 

 barium sulphate. The serum, however, may be heated to 100 

 degrees in such a way as to preserve its dissociating property almost 



ting properties of serum were due, then, to different substances, we should be able 

 to remove the first by a small dose of barium sulphate and thus leave the second 

 intact. We may then treat a given amount of heated serum with an amount of 

 sulphate which is just sufficient to remove its cloudiness; in this way we remove all 

 the agglutinating properties, but we find that no trace of dissociating property 

 reappears. 



We conclude, then, that the two different actions of serum on barium sulphate 

 are due to the same substance which becomes changed by heat. 



* There is an evident resemblance between this fact and the observation of 

 Henri and Mayer, who found that the clumps resulting from an agglutination of 

 two colloids of different charges become dissolved in an excess of one or the other 

 of these colloids. 



* Henri and Mayer. Soc. de Biol., 1904, No. 19. 



