1923] 



JENNISON — POTATO BLACKLEG 39 



The writer's conclusion is based upon the results of carefully 

 conducted quantitative determinations of carbohydrate hydroly- 

 sis by certain of the blackleg strains at hand. In this phase 

 of the work the hydrolysis of potato starch, as well as other 

 carbohydrates, was investigated. No evidence was found of the 

 slightest hydrolysis of potato starch by the blackleg bacillus 

 after an interval of 6 days. The ordinary tests for diastatic 

 action were made, using a nutrient agar starch jelly, and these 

 yielded no evidence of diastatic action. These results are not 

 in accord with those of most investigators (table vi). 



Active acidity and titratable acidity of culture solutions. 



While the greater part of the experimental work reported 



here was done in 1916 and 1917, the data presented in this sec- 

 tion were obtained in May, 1922. Experiments were made in 

 order to determine the production of acid, as shown by the de- 

 termination of H-ion concentration, as well as by the relative 

 amount of titratable acid produced by Bacillus atrosepticus when 

 cultivated in the presence of certain sugars. Subcultures of 

 strain No. 196 were employed in these experiments. 



To a nutrient broth made as before 1.0 per cent of the follow- 

 ing sugars was added: (a) glucose ["Difco"], (b) sucrose 

 [Merck's highest purity], (c) lactose [Merck's]. 



Cultures and methods.— Comparatively large-volume cultures 

 were employed, 500 cc. of each of the sugar broths being placed 

 in each of 3 Florence flasks of 1 liter capacity. Sterilization was 

 accomplished in the autoclave at 15 pounds pressure for 15 

 minutes. In order to avoid the lag phase of growth (Chambers 



the sugar broth employed 



old was used 



The H-ion concentration of each culture medium was deter- 

 mined at the time of inoculating the sugar broths and thereafter 

 as indicated (table vn). The colorimetric method of Clark and 

 Lubs ('17) was employed. The production of titratable acid 

 was determined in the usual manner, using 0.507 NaOH and 

 phenolphthalein, and the amount of titratable acid was expressed 



in degrees on Fuller's scale where "+10"=0.1 of 1 per cent 

 normal HC1. 



Buffer index.— Following the method of Brown ('21) the buf- 

 fer index of the medium was determined in order to provide 



