THE RELATION OF SURFACE TENSION TO BACTERIAL DEVELOPMENT

Abstract

The depressant used consisted of 4 soaps prepared from castor oil, cocoanut oil, olive oil and palmitic acid; 2% stock solutions of each were prepared and added by pipette in the desired ampurit. The medium consisted of glucose beef infusion broth made from "difco" peptone, without NaCl. Preliminary experiments indicated that when the medium was stirred just before making the readings, the surface tension constant could be determined with 2-3 readings; when not stirred it frequently required as many as 9. The 1st method also resulted in higher readings, due to uniform dispersion of the depressant; with the 2nd method the depressants were concentrated at the surface. All measurements recorded were made after stirring the medium to the point of equilibrium, and most of them are in terms of the data secured by the film method. The latter gave constantly lower results than the drop weight method. Diplococcus pneumoniae, Streptococcus viridans, Streptococcus he-molyticus and 4 strains of Staphylococci were grown in broths having various surface tensions. Considerable variation in growth was observed in the broths containing depressants. In general, there was a marked inhibition during the first 24 hours, which was in many instances largely overcome within 3 days; in few cases did growth equal that in controls. Inhibition was not directly associated with surface tension. In many instances, greatest inhibition occurred at higher surface tensions, while broths of lower surface tension gave maximum development in the reduced series. This indicates that inhibition was due to the chemical nature of the depressant rather than to reduced surface tension. Within the experimental limits, there was nothing to indicate that surface tension is a factor in the development of the organisms studied.