J. RUSSELL ESTY 



293 



Whitworth' states that the heat resistance of B. anthracis is influenced by the hy- 

 drogen-ion concentration and the composition of the medium in which they are sus- 



. M . 



pended. Anthrax spores suspended in - phosphate mixtures show greater resistance 



at 85° C. than those in broth or in broth to which 3 per cent gelatin has been added. 



CHART I 



Resistance or B. botulinus Spores in Phosphate Mixtures, Veal Infusion of Varying pH 

 Values by the Addition of Acid or Alkali, and Food Juices. 



He also noted that the optimum pH was about 7.0 at 85° C, and that the decrease of 

 resistance is more marked on the acid side. 



Another factor which influences the resistance has been frequently overlooked. 

 Esty and Cathcart^ found that heating unbuffered solutions in soft-glass tubes changes 

 the hydrogen-ion concentration. Mixtures of Na2HP04 and KH2PO4 in hard-glass 

 tubes were not altered when subjected to high temperatures, although prolonged 

 heating in soft-glass tubes dissolved alkali in excess of the amount which can be con- 

 trolled by the buffer salts. 



' Whitworth, S. H.: Thesis, Inst. Veterinary Pathology, University of Zurich. Jan., 1924. 

 ^ Esty, J. R., and Cathcart, P. H.: /. Infect. Dis., 29, 29. 1921. 



