Effect of Acids on Typhoid and Colon Bacilli 279 



its water value. The toxicity of benzoic acid, measured in normality, 

 is diminished under the same conditions to from one-fourth to one- 

 half, and that of acetic acid to a little over one-half its water value. 



The most probable explanation of this phenomenon is the forma- 

 tion of a loose compound between the proteid molecules and the acids 

 which would diminish the toxicity of the latter, just as Stiles and Beers 

 (1905) have shown that such a combination alters the effect of 

 mineral salts on muscle. 



Bugarzky and Liebermann (1898), Cohnheim and Krieger (1900), 

 and other observers, have proved the existence of such loose com- 

 pounds between proteids and acids by freezing-point determinations. 

 We desired, however, to examine the actual substance used in our 

 own experiments. Through the kindness of Dr. Raymond Haskell, 

 of the Research Laboratory of Physical Chemistry of this Institute 

 determinations of electrical conductivity were made on the peptone 

 solution used in our experiments, on a solution of hydrochloric acid 

 in distilled water, and on a solution of the same strength in the pep- 

 tone solution. 



The specific conductivity of the peptone solution was 0.000.^, 

 showing that it was fairly pure. That of the hydrochloric acid solution 

 0.02 normal or 720 parts HCl per million, 90.46 per cent dissociated, 

 was 0.007. The I per cent peptone solution containing 0.02 normal 

 hydrochloric acid gave a conductivity of 0.002, showing that approxi- 

 mately four-fifths of the hydrochloric acid had been neutralized by 

 the peptone. 



It is evident that the effect of the peptone in decreasing the toxicity 

 of the hydrochloric acid may be explained by the fact that the numlx-r 

 of dissociated hvdrogen ions is decreased by the peptone in the same 

 degree. The effect would naturally be less marked, as we find to be 

 the case, with sulphuric acid, since this acid is less ionized to start 

 with. Finally, the un-ionizcd organic acids are least affected. The 

 decreased toxicity which does occur with them may perhaps be due 

 to a loose compound with their whole-molecule — what Stiles and Beers 

 call a "physiological compound." 



6. GENER.\L CONCLUSIONS. 



It appears from our experiments that the typhoid bacilkis is highly 

 sensitive to an excess of acid, being destroyed in an aqueous suspen- 



