118 BIOLOGY OF PNEUMOCOCCUS 



this phase of the biology of Pneumococcus, if they have not al- 

 ready been made, should be undertaken because of the additional 

 information which may accrue. 



Classification According to Electrophoretic Potential 

 Another criterion for classification, other than agglutination or 

 protection tests, was advanced by Thompson (1931). 1396 By deter- 

 mining the electrophoretic rate of migration, he grouped the sixty- 

 seven strains studied into five groups. The A group included typi- 

 cal Type Ill's and one Group IV strain. Group B consisted of 

 typical Type I strains and a few Group IV strains. C took in Group 

 IV strains, an atypical III, and two atypical II organisms. D was 

 represented by a typical Type II, a few of Group IV, and one 

 atypical Type I strain, while E was represented by only two 

 Group IV strains. Since Groups C and D were shown not to be 

 definitely distinct from each other and since the number of strains 

 comprising Group E was too small to be significant, there remain 

 only three large electrophoretic groups. In a second paper, Thomp- 

 son 1397 presented data on the rate of migration in the electro- 

 phoretic field and the isoelectric points of various pneumococcal 

 strains, but made his classification somewhat unwieldy by the addi- 

 tion of intermediary groups. While knowledge of the differences in 

 the electrophoretic potential of different strains of pneumococci 

 may be of scientific interest, the method has no advantage over the 

 serological classification. 



We are now learning of yet wider deviations from special specifi- 

 cations than those we have already discussed. At first sight they 

 seem to confuse the definite lines of demarcation that have been 

 drawn between bacterial species and the still finer distinctions that 

 have been established on both chemical and serological grounds for 

 types within the species. Pneumococcal cells possess polysaccha- 

 rides peculiar to each type, and the carbohydrate is looked upon 

 as the factor that determines the exact place of a Pneumococcus 



