BY R. GREIG SMITH. 605 



Production of Acid by Kaces Grown for Seven Days at 37*^. 



It is evident from these results that the production of acid by 

 the races is variable, and beyond the acidity being equal to 

 between 0*06 and 0-13 % lactic acid, there is little to be inferred. 

 Repeated cultivation of the races in the laboratory has no definite 

 effect upon the acid-forming faculty, since in one case the culti 

 vation has lessened the production, and in two others there is 

 little difference. The amount of peptone in the nutrient fluid 

 has a considerable influence upon the formation of acid, as was 

 found in the experiments noted on page 596. AVith 0*01 % of 

 peptone, the acidity on the fifth day was equal to 0-03 % lactic 

 acid, while with 1 % of peptone the acidity was 0*18 %. 



The Nature op the Acids. 



In determining the nature of the acids a considerable number 

 of cultures were made and tested. These were chiefly tentative 

 or preliminary, and served to indicate the kinds of acids present 

 and also the method which appeared to be best for their separa- 

 tion. Ultimately the following method was adopted : — 



Two litres of the ordinary 10 % saccharose medium containing 

 100 grms. of chalk was infected with a mass culture (about 50 c.c.) 

 of the organism and incubated at 37°. The culture was vigor-, 

 ously shaken every morning and the incubation was continued 

 for a month, when it was noted that the evolution of gas bubbles 

 had ceased. The culture was then treated in the manner 

 described in the followino- table. 



