UNSOLVED PROBLEMS 615 



ally transform the degraded variant into a member of a different 

 serological type, invites further study. 



Does dissociation of pneumococci proceed in the animal body? 

 At present the answer is, Probably not ; but the manner in which 

 the many types of pneumococci have arisen may some day be dis- 

 covered to be related to the influences that cause variation, rever- 

 sion, and transformation of type. 



The supposition that the close relation apparently existing be- 

 tween pneumococci and streptococci denotes a divergent evolution 

 from a common progenitor does not bear analysis in a genetic 

 sense. Bacteria are unicellular organisms reproducing by the ele- 

 mentary process of fission and it is far more likely that environ- 

 mental influences induce or result in more or less transient physio- 

 logical or protoplasmic changes that are wholly or in part 

 reversible when the cells grow under other conditions. The recogni- 

 tion of the stability of biological types or species, therefore, leads 

 rather to continued study of the cultural factors that bring about 

 temporary modifications in bacterial characters. 



CHEMICAL CONSTITUENTS OF PNEUMOCOCCI 



The knowledge gained in the last score of years concerning the 

 chemical nature of the components of the pneumococcal cell fur- 

 nishes abundant material for a broad program of future bio- 

 chemical and immunological studies. How closely do the proteins 

 and polysaccharides thus far isolated correspond in molecular 

 configuration to the parent substances as they exist in the living, 

 intact cell? What are the relationships between chemical consti- 

 tution and biological specificity? What is the exact grouping and 

 what are the linkages of radicals that determine for a strain its 

 type-identity? Are there actually antigenic and haptenic groups 

 in some of the specific carbohydrates, or are antibody stimula- 

 tion and antibody combination only quantitative manifestations of 

 the same phenomenon? How can one account for the partial sero- 



