1923] 



JENNISON — POTATO BLACKLEG 29 



Cultural features and physiology. — In prosecuting the general 

 plan outlined for making comparative studies of the cultural 

 features and physiology, it was deemed wise to give particular 

 attention and painstaking effort to the study of those items 

 which are most commonly made use of in establishing bacterial 

 species. 



In recent times the response of the microorganism, as well as 

 the reactions set up by it, in the presence of carbohydrates, has 

 been stressed in attempts to distinguish between closely related 

 species. On this account, and because of the fact that earlier 

 students of the potato blackleg parasite report a great variety 

 of conclusions as to the ability of this organism to ferment cer- 

 tain carbohydrates, the writer made exhaustive studies upon the 

 gas- and acid-producing function of the blackleg bacillus. De- 

 tails of the comparative studies appear on the several tables pre- 

 sented herewith and in the paragraphs below. 



Nutrient broth: — Clouding prompt, persistent; medium becoming 

 slightly turbid ; sediment compact, granular, somewhat viscid ; surface 



growth a ring, though under certain circumstances a light pellicle may 

 form ; no chromogenesis ; odor absent ; color of medium unchanged. 



Earlier students of the blackleg bacillus did not wholly agree 

 as to cultural features exhibited by this organism when grown in 

 nutrient broth. The several strains studied were grown in 3 

 nutrient broths: (A) "Bacto" beef and "Bacto" peptone, (B) 

 Liebig's beef extract and Witte's peptone, (C) fresh meat infu- 

 sion and Witte's peptone, and all incubated at 27-28° C. All 

 (except No. 191) were very similar in their response in nutrient 



broth. In those grown in "Bacto" beef and "Bacto" peptone 

 (except Nos. 191 and 198) the surface growth was a ring, cloud- 

 ing was moderate, sediment granular-viscid, the medium slightly 

 turbid, and no color. In the case of 191 the surface growth was 

 a membrane, and in 198 a light pellicle with moderately strong 

 clouding. When the strains were grown in Liebig's beef extract 

 and Witte's peptone the surface growth was a ring (except No. 

 191 which was a membrane), clouding moderate, sediment gran- 

 ular viscid, medium slightly turbid, chromogenesis none. In 

 those grown in fresh meat infusion and "Bacto" peptone, ex- 

 cept Nos. 160.1 170.3, 187B.1, 191, 197, and 201, the surface 

 growth was a pellicle, the clouding strong, the sediment granular- 

 viscid, medium slightly turbid, and chromogenesis none. Nos. 

 160.1 and 187B.1 showed the surface growth a wide ring, and 



