ON THE MODE OF ACTION OF PREVENTIVE SERA. 95 



between bacterial species that are so difficult to define and separate, 

 would scarcely appear to be in harmony with our present knowledge 

 of the origin of species. Moreover, we know that the vibrio of 

 Massaouah, which is certainly a cholera vibrio, does not show the 

 granular change with cholera serum. The method, however, in 

 many instances may be of real value and aid considerably in 

 confirming the diagnosis. 



Instead of injecting vibrios and serum into the peritoneal cavity 

 of an animal, there is a simpler method, which we have described as 

 a modification of the Pfeiffer diagnostic procedure, and which con- 

 sists in making a mixture of the vibrio and fresh preventive serum 

 in vitro (in case the preventive serum is not fresh, fresh normal 

 serum may be added). If the organism is susceptible to the action 

 of the serum, in other words, if it belongs to the strain against which 

 the animal that has furnished the serum has been vaccinated, it 

 will lose its motility by clumping and show granular transformation 

 as already described. We described this procedure in vibrios only, 

 whereas Pfeiffer has applied his method not only to vibrios, but to 

 the colon bacillus and the typhoid bacillus as well. 



Gruber and Durham make a diagnosis, not only between vibrios, 

 but even between B. coli and B. typhosus, using as the single 

 criterion the immobilizing and clumping effect which each specific 

 serum shows for its respective micro-organism. For example, it is 

 assumed that a suspension contains typhoid bacilli if the organisms 

 in it are clumped by antityphoid serum. 



As far as vibrios are concerned Gruber and Durham's method is 

 only a mutilation of our own in- vitro method. Our method, as we 

 have just described it, gives three distinct indications of the reaction 

 of the bacteria in question to the serum that is used. These indica- 

 tions are loss of motility, clumping, and granular transformation. 

 Gruber and Durham pay no attention to this latter important indi- 

 cation and consider only the first two. A priori it would seem 

 impossible to have too many distinctive indications in dealing with 

 a task so delicate as a diagnosis between two closely related species 

 of bacteria, and it would seem that ignoring one of these indicat- 

 ing signs would scarcely constitute progress. In other words, we 

 should consider all the indications of specificity that our data may 

 afford us. 



