368 



[Vol. 9 



ANNALS OF THE MISSOURI BOTANICAL GARDEN 



Acid 



Acetic 



Citric 



Hydrochloric 



Lactic 



Malic 



Phosphoric 



Tartaric 



TABLE VI 



ACID BROTHS WITH ALKALI ADDED 



Per cent 



0.05 

 0.1 



0.1 



Ph after addition 

 of alkali 



7.0 

 5J 



6.0 



7.4 



7.0 



6.0 

 7.0 



5.8 



6.2 



Growth at end 

 of 10 days 



Good 



None 



Good 



Good 



Good 



Good 

 Good 



Good 



Good 



has any poisonous action in the concentrations used (see account 

 of growth in Fermi's solution). Of course, the undissociated 

 molecule may play the role of poison but this also fails to give a 

 convincing explanation of the action. The specificity of the or- 

 ganism with relation to phosphate may be a factor but this is 

 merely assumption; there may be some chemical rearrangement 

 involved which has not been previously recognized, or the action 

 may be a physical one involving such phenomena as surface ten- 

 sion. Traube (II, '21), for example, believes that surface tension 

 should be considered as entering into the action of acids and 

 bases. 



In order to test the effect of autoclaving, acids were added 

 to the medium before sterilizing. Approximately 15 pounds pres- 

 sure for 20 minutes was used. The following acids were em- 

 ployed: citric, hydrochloric, lactic, malic, phosphoric, and tar- 

 taric. They were added to nutrient broth in amounts so as to 

 make 0.1 and 0.2 per cent by volume. In every case the hydro- 

 gen-ion concentration, ascertained after sterilizing, was the same 

 in each acid, and at both 0.1 and 0.2 per cent it was Ph 5.2. 

 (The nutrient broth in this case contained dehydrated beef in- 

 stead of Liebig's beef extract, which was used in the acid experi- 

 ments previously reported.) No growth was obtained in any 

 of the acid media, either at 0.1 or 0.2 per cent, while the same 

 medium without acid showed excellent growth. 



Comparison between cotton and glass wool as filtering agents. — 

 In 1916 Miss Lloyd reported that certain substances necessary 

 for growth of Meningococcus were removed when filtering was 



