92 STUDIES IN IMMUNITY. 



study the clumping produced by specific sera in organisms other 

 than the vibrios. If, for example, we examine the clumps of tetanus 

 bacilli which are well formed by the action of an antitoxic horse 

 serum, we find that the bacteria, although collected in small masses, 

 do not adhere well. A similar fact is suggested on examination of 

 stained preparations of masses of vibrios. The preparations made 

 from a clumped culture of tetanus suggest in appearance a handful 

 of pins that has been carelessly thrown on a table. The clearly 

 defined stiff rods cross each other in all directions without giving 

 evidence of an intimate contact, and with rather large spaces 

 between them. The appearance of the bacilli is absolutely normal, 

 even when they have remained for a long time in the serum. An 

 examination of clumped streptococci gives similar results. Clump- 

 ing may be noted also in cells other than bacteria. Red blood cor- 

 puscles, for example, may show it very distinctly. If a small amount 

 of rabbit serum is added to guinea-pig serum containing a few blood 

 corpuscles the latter very rapidly undergo a curious modification; 

 instead of remaining scattered uniformly throughout the fluid they 

 collect in perfectly definite clumps which stand out as little red 

 points in a clear liquid. 



But if instead of using rabbit serum, we add the serum of one 

 guinea-pig to the corpuscles of another, no change takes place in the 

 uniform turbidity of the fluid. Horse serum when added to red 

 blood corpuscles of the guinea-pig or of the rabbit clumps them 

 energetically. In a similar manner rat serum clumps rabbit cor- 

 puscles and vice versa; goat serum produces the same effect on 

 guinea-pig corpuscles. These facts would indicate that as a general 

 rule red blood corpuscles are clumped by serum from a different 

 animal species. 



It may be added that the cholera vibrio, when cultivated in 

 guinea-pig serum containing corpuscles, clumps them. It would be 

 interesting to ascertain whether red blood corpuscles subjected to 

 the effect of foreign serum, or taken from an infected animal, still 

 show normal osmotic properties and act in the usual manner with 

 salt solutions. 



There is a striking analogy between the clumping of red blood 

 cells by a foreign serum and the effect of preventive serum on bac- 

 teria. If we imagine that bacteria swell up and become viscous 



