153 



In Jan. 1920 I made plates of agar with only 0.2o/ dissolved blood 

 cells having 11 different reactions; to 50c. c of the original agar 

 were added (1) 0.05, (2) 0.04, (3) 0.03, (4) 0.02, (5) 0.01 c.c. concen- 

 trated hydrochloric acid, (6) none, and to (7) 0.1, (8) 02, <9) 0.3, 

 (10) 4, and (11) 0.5c.c. n. NaOH. No. 4 reacted neutral to azolit- 

 min paper, and the colorimetric determination of No. 11 partly 

 with neutral red and partly with a-naphthol-phlhalein gave Py. -— 7.6 

 (circ). Attempts to an exact colorimetric determination of rhe reac- 

 tion of the different media gave no trustworthy results. On the 

 media Nos. 1, 2, 4, 6, 8, 9, 10, and 11 all the strains on p. 108 

 were inoculated with the result that after IV2 days in the incubator 

 none of them grew on No. 1 ; on No. 2 all the strains with the 

 exception of I 5 grew, but very poorly; on No. 4 all the strains 

 gave a very fair growth, but weaker than on Nos. 6, 8, 9; 10 and 

 11. On these last 5 plates the growth was about equal (conside- 

 rably weaker than on agar with an abundant supply of haemoglo- 

 bin. Perhaps it was a trifle better on No. 10 than Nos. 6, 8. 9. 

 and 11. On examining them again after a further 24 hours in the 

 incubator no marked change was observed. 



This experiment teaches that all the strains behaved in a similar 

 manner with regard to dependence on hydrogen ion concentration; 

 anv marked individual differences could not be demonstrated. 



Minimum Temperature for Growth. 



The temperature limit for growth must undoubtedly be 

 reckoned as one of the most constant characteristics of the 

 different bacteria, and I have therefore investigated it for a 

 large number of strains of Pfeiffer's bacillus, but only as re- 

 gards the lowest temperature limit, where it might be as- 

 sumed that any differences would be most marked, and where 

 the determination from a technical point of view, was easiest 

 to carry out. The results are tabulated below. 



