62 



Scientific Proceedings (117). 



32 (i779) 



Rapid determination of surface tension. 



By ROBERT G. GREEN (by invitation). 



[From the Department of Bacteriology, University of Minnesota, 

 Minneapolis, Minn.] 



An apparatus was demonstrated by means of which the surface 

 tension of a liquid is rapidly determined by the drop-weight 

 method. From one to six drops of the liquid to be measured is 

 required. The apparatus consists essentially of a delicate torsion 

 wire balance and an adjustable scale on which the surface tension 

 is read in dynes per centimeter. 



33 (i78o) 



The influence of the surface tension of the culture medium on 



bacterial growth. 



By W. P. LARSON. 



[From the Department of Bacteriology, University of Minnesota, 

 Minneapolis, Minn.] 



Pellicle-forming bacteria such as the B. tuberculosis, B. subtilis 

 and others of that group which habitually grow upon the surface 

 of liquid medium, will grow throughout the body of the medium 

 by depressing its surface tension from 59 dynes, the S. tension 

 of ordinary broth, to 40-45 dynes. By analogy with the floating 

 needle experiment it may be assumed that when the pellicle-form- 

 ing bacteria are properly wetted they no longer grow upon the 

 surface of the medium but throughout the body of the broth or 

 even at the bottom of the flask. 



The further observation has been made that the B. subtilis 

 and B. anthracis, when grown in media of low S. tension, finally be- 

 come asporogenous. Cultures of B. anthracis grown under such 

 conditions and sterilized by heat at 6o° for 30 minutes protect 

 guinea pigs. The enhanced wetting of the bacteria brought about 

 by the addition of soap probably creates better nutritive condi- 

 tions which cause the organisms to grow without forming spores. 

 Castor oil soap when in aqueous solution is perfectly clear, does 



