THE PRECIPITINS 227 



culture of typhoid bacilli and filtered it to remove the bodies of 

 the bacteria, and then added some typhoid serum to the clear 

 solution, a precipitate was formed. The same happened with 

 cultures of cholera and plague organisms, after addition of the 

 appropriate sera, so that the reaction is, within limits, specific. 

 The limits of the specificity are not yet thoroughly ascertained, 

 but there are distinct evidences of group reactions similar to those 

 seen in the agglutinins. Thus Norris found a common precipitin 

 for organisms of the cholera group, for some cocci, etc. There 

 were, however, some exceptions ; thus, a rabbit which had been 

 injected with cultures of B. prodigiosus developed a precipitin which 

 acted on filtered cultures of B. coli and V. Metchnikovi, as well as 

 on the filtrate from the organism injected. He thought, however, 

 that the reaction is a more intimate and constant test of group 

 relationships than is agglutination ; thus he prepared an antiserum 

 to a bacillus belonging to the hog-cholera group which did not 

 agglutinate typhoid or colon bacilli, but which gave the precipitin 

 reaction with their filtrates. The bacillus, it may be pointed out, 

 is a member of the same group as the other two, so that (in the 

 case of this particular serum) the agglutination reaction is mis- 

 leading. 



Bacterio-precipitins may be prepared by the injection of cultures 

 of the bacteria, or the filtrates from the old cultures spoken of 

 above ; it is evident, therefore, that they are antibodies to substances 

 in solution. Some authorities, it is true, have thought that the 

 actual antigen and precipitable substance consist in reality of the 

 broken-off flagellae, which are sufficiently fine to pass through a 

 Berkefeld filter ; but this can hardly be the case, since a bacterio- 

 precipitin can be obtained for non -flagellate organisms. It is true 

 that the best-known and most powerful of these antibodies are for 

 organisms which possess flagellae, and it is quite probable that the 

 clumping of these filaments does occur in some cases, and intensi- 

 fies, or may be mistaken for, a true precipitation. 



Bacterio-precipitins cannot be (or have not been) prepared to all 

 organisms. Thus, diphtheria antitoxin does not form a precipitate 

 with diphtheria toxin, a substance prepared on lines exactly similar 

 to those used in procuring the precipitating solution for typhoid 

 and cholera. Diphtheria toxin is an excreted substance, not a 

 substance dissolved out of the bacterial protoplasm. 



The first to observe precipitins to other proteid solutions, and in 

 particular to serum, was apparently Tchistovitch, in 1898. He 



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