STREPTOCOCCUS HEMOLYTICUS 203 



who accordingly divided the acids used into three classes based 

 upon their ionization constants and similarity in toxicity. Sur- 

 prising differences in the toxicity of various acids for molds were 

 found by J. F. Clark (1899) in 1899. The degree of dissociation 

 seemingly stood in no relation to the toxicity and this observer 

 was forced to the conclusion that the inhibitory property, for 

 molds at least, resided largely in the undissociated molecules. 



The approximate concentrations of a number of common 

 inorganic and organic acids required to inhibit growth of Strep- 

 tococcus pyogenes have been determined by Taylor (1917) in the 

 course of studies on the disinfection of war wounds. Consider- 

 able variation in potency was apparent with the organic acids 

 investigated though apparently no account was taken of their 

 degrees of ionization. 



Wolf and Harris (1917a) in their study of the effect of acids 

 upon the fermentations of Clostridium welchii and C. sporogenes 

 point out that the influence is two-fold; first, that exerted by the 

 hydrogen-ions, and second, that due to the anions and undisso- 

 ciated molecules. Lactic acid was found to have about the 

 same toxicity as hydrochloric, whereas acetic, succinic, and 

 butyric inhibited growth at lower hydrogen-ion concentrations 

 (higher Ph). Wyeth (1918) reported similar results with Bad. 

 coll. He points out that if the actual mass of acid be considered 

 hydrochloric was more inhibitory than lactic or acetic acids 

 but that the lethal points of such organic acids, in terms of 

 hydrogen-ion concentrations, were lower than that of hydro- 

 chloric. In equivalent quantities the highly ionized acids 

 proved more effective in inhibiting growth. 



Lord (1919), has obtained data which lead him to believe 

 that acidity is the principal inhibitory factor in glucose broth 

 cultures of pneumococcus, though H.M.Jones (1920) very recently 

 has succeeded in demonstrating that in the presence of body 

 fluid such as blood serum or ascitic fluid the tolerance of this 

 organism for hydrogen ions is considerably increased. This 

 same phenomenon had been noted previous to the appearance of 

 Jones' article during the course of the present investigation 

 upon Streptococcus hemolyticus and the facts have proved so 



