EXPERIMENT STATION REPORTS. 193 



aud 0.005 cc. The tii'bes were incubated at 37° C for eighteen hours 

 and the results recorded as follows : -|- = complete clumping, P = 

 incomplete clumping and o = no clumping. The degrees of incomplete 

 clumping are not recorded here as it is doubtful if any two workers 

 would read the degree of clumping alike. 



Results of Study. 



Table II illustrates the degree of agglutination of twenty-one strains 

 of Bad. abortus by fifteen different bovine sera, fourteen of which were 

 from animals which had aborted from a natural infection, and one, 

 numlber 1, had no history of ever being infected. Incidentally, the con- 

 centration of agglutinins in each serum examined varied widely. Such 

 variations are of considerable aid in separating out slightly different 

 groups of the organism. A "pro-agglutinating" serum (No. 10) was 

 encountered at this time and introduced into the group. There was 

 little or no difference in the degree of pro-agglutination for the several 

 antigens employed. In studying this phenomenon, it was found that if 

 the density of the antigen was lowered the dilution of serum in which 

 pro-agglutination occurred was increased, but if the density was in- 

 creased to a certain degree the negative has disappeared, and complete 

 agglutination occurred in all tubes. 



It is evident from the tabulated results that there is no difference in 

 the aggiutinability of the several cultures of Bad. abortus : occasion- 

 ally a serum would fail to agglutinate one or two strains to the same 

 degree, but as these results would often be reversed in other sera, it was 

 decided that the variations were due to the failure of placing the exact 

 amount of serum in similar tubes. The failure of serum number 11 to 

 agglutinate a single antigen is of considerable importance as it gave a 

 complete fixation of complement in 0.005 cc. The sample w^as taken 

 from a cow shortly after abortion. 



The group to which Bad. meUtcnsis I. belongs is not known. It may 

 be noted that it is only appreciably agglutinated by sera from animals 

 infected with Bad. abortus. Baet. melitensis No. 7 belongs to Group 

 II, and 22 to Group IV as found by Fusier and Meyer (1). Bad. 

 melite^hsis 27 appears to be agglutinated by all sera to the same degrea 

 as the strains of Bad. abortus, while 22 was not clumped by a single 

 serum. 



The aggiutinability and the pathogenicity of Bad. abortus appear to 

 be separate and distinct properties, neither of which is indicated by the 

 other. Old, non-pathogenic strains are as agglutinable as newly iso- 

 lated strains. 



