322 STUDIES IN IMMUNITY. 



adding 5 drops of olive oil to 10 c.c. of distilled water plus 

 0.001 of a cubic centimeter of sodium carbonate. Such feebly 

 alkaline emulsions may be neutralized or even acidified without 

 showing any change. In our experiments we have used such 

 emulsions neutralized as carefully as possible. Working with them 

 we find that the tiny drops of oil agglutinate on the addition of 

 suspensions of CaFl 2 and barium sulphate and also of colloidal 

 ferric hydrate. The flocks obtained in this manner are found 

 microscopically to consist of a suspension of the hydrate with drops 

 of oil scattered among them. It is found, moreover, that the addi- 

 tion of a small amount of serum prevents the agglutination of 

 oil corpuscles by suspensions and by ferric hydrate in the same 

 way as it does the agglutination of red blood cells by chemical 

 precipitates. 



Inasmuch as these two forms of agglutination apparently agree, 

 we believe that their respective causes are due to the same factors 

 and that the agglutination of red blood cells by suspensions and 

 colloids is not an indirect result of the effect of electrolytes on 

 these suspensions, but due to a direct effect of one element on the 

 other. 



We have just seen that certain suspensions agglutinate blood 

 cells. If in place of the corpuscles we add serum to either of these 

 two suspensions we find that CaFl 2 becomes clumped, while barium 

 sulphate is unaffected. Suspended in salt solution barium sulphate 

 sediments rapidly to the bottom of the tube. In serum, on the con- 

 trary, it does not fall or falls only very slowly, and remains in the 

 fluid in the form of a fine suspension. This dissociating effect of 

 serum on barium sulphate is very marked and evident even on 

 the addition of 1 drop of serum diluted 1-20 to 1 c.c. of 0.8 per 

 cent salt solution containing 4 drops of an emulsion of barium 

 sulphate. 



We have then, on the one hand, an agglutination (barium sul- 

 phate plus corpuscles) and on the other hand quite a different 

 phenomenon, namely, a dissociation of the suspension (barium 

 sulphate plus serum). It is generally supposed that the albuminous 

 substances of serum are in a state of colloidal solution. An emul- 

 sion of corpuscles, then, is the same as serum in that both are emul- 



