362 APPLICATION OF METHODS OF BACTERIOLOGY 



tributed helpful information to our general comprehension 

 of the subject. 



The conception that streptococci forming long chains 

 are more often pathogenic than those forming short chains is 

 not always a trustworthy criterion ; and the differences in the 

 action of different streptococci upon particular ingredients 

 of special culture media has helped, but not enough for 

 satisfactory grouping. 1 



The discovery that the majority of streptococci associated 

 with serious pathological phenomena have the power of 

 hemolyzing blood, while others do not possess this function 

 is a great step in advance, but unfortunately for the sim- 

 plicity of the matter we find such differences among those 

 hemolyzing or hemolytic streptococci as to make further 

 subdivision (classification) of the group desirable. 



With this in mind recent studies by a number of investi- 

 gators have contributed information of the greatest practical, 

 as well as theoretical, value. 



As in the case of the pneumococci (which see) there is 

 now an agreement of opinion that differentiation of these 

 closely allied varieties of pathogenic organisms is best 

 accomplished through specific immunologic reactions, and 

 to this end the agglutination test made with the serum of 

 immunized animals seems to prove trustworthy; though as 

 yet there have not been established such definite groups 

 or types as has been done with the pneumococci. 



If, for instance, any given group of hemolytic strepto- 

 cocci be obtained from different diseases and an animal 

 be rendered immune from one of them by appropriate 

 means, the serum from that animal will certainly agglu- 



1 See The Use of Blood Agar for the Study of Streptococci, Monograph 

 No. 9, Rockefeller Inst. Med. Research, January 21, 1919. 



