34 



Scientific Proceedings (117). 



blood similar to those noted when the cure is effected by cod liver 

 oil. This is of interest as affording testimony that the curative 

 process occasioned by these divergent therapeutic agents is funda- 

 mentally the same. These observations establish a chemical basis 

 for heliotherapy in rickets. They furnish also, as far as we know, 

 the first definite evidence of metabolic change in the animal body 

 brought about by the solar rays. 



17 (1764) 

 Dissociation of microbic species. 



II. Mutation in pure-line strains of the bacillus of 

 rabbit septicemia. 



By PAUL H. DE KRUIF. 



[From the Laboratories of the Rockefeller Institute for 

 Medical Research, New York City.] 



The coexistence of two distinctly different types of microbe in 

 cultures of the rabbit septicemia bacillus has been reported in a 

 previous paper. 1 These varieties, once separated, appear to 

 breed true to type for many passages. The organisms have been 

 designated as types D and G. Type D is very virulent for rabbits, 

 grows diffusely in liquid media, and yields highly fluorescent, 

 rather opaque colonies on serum agar. Type G is of extremely 

 low virulence, exhibits a granular sedimenting growth in fluid 

 media, and grows in the form of translucent, non-fluorescing 

 colonies on serum agar. The two types show no noticeable dif- 

 ferences in morphology or in fermentation reactions. Immuniza- 

 tion and agglutination reactions indicate their antigenic com- 

 munity. 



It seemed necessary to determine whether the two varieties 

 coexist in cultures isolated from infected rabbits or whether one 

 variety arises from the other. Type D (virulent) is the microbe 

 invariably obtained from the naturally infected rabbit. Type G 

 has only been found after artificial cultivation has been carried 

 on for some time. But since the primary isolations were made 

 from colonies which conceivably might arise from two or more 



1 Jour. Exper. Med., 1921, xxxiii, 773. 



