264 C.-E. A. WiNSLOW AND E. E. LOCHRIDGE 



on the seedlings of higher plants. In Clark's experiments it proved 

 far more fatal than any other acid, being 70 times as active as 

 hydrochloric. The molecule at the concentrations used is probably 

 only slightly dissociated. 



In some ways the most important work upon this subject was 

 the very careful study made by Bial, of the antiseptic action of the 

 hydrogen ion of dilute acids upon yeast. He first became interested 

 in the problem from a consideration of the causes which allow pro- 

 duction of gas in the stomach, and carried out his earliest experiments 

 by observing the gas formation in yeast cultures in the presence of 

 various substances present in the normal gastric juice. This series 

 of studies (Bial, 1897) showed that the presence of albuminoid 

 substances or of sodium chloride effected a marked restriction of 

 the antiseptic action of hydrochloric acid. Bial at this time did not 

 apply physico-chemical theories to the explanation of these phenom- 

 ena; but in another contribution he made a fuller study of the 

 problem. His later experiments (Bial, 1902) were again made with 

 yeast cells, cultivated in fermentation tubes filled with grape-sugar 

 solution to which various amounts of acid had been added; the 

 antiseptic action was inversely registered by the amount of gas 

 produced. The advantage of this method is its great delicacy; 

 the fermentative power of the yeast responds to such extremely 

 minute quantities of acid that the ionic effects are not complicated 

 by other actions which appear in stronger solutions. Bial did not 

 make exact calculations of the amount of dissociated hydrogen 

 necessary to inhibit the yeast, but he found that a general relation 

 existed between the ionization and the antiseptic action. The 

 strongly dissociated acids — hydrochloric, sulphuric, nitric, and 

 trichloracetic — entirely stopped the action of the yeast in concentra- 

 tions of between 0.005 ^^d 0.008 normal. Acids of an intermediate 

 grade — phosphoric, formic, and oxalic — accomplished the same effect 

 when o.oi normal; while acids still less dissociated — acetic, benzoic, 

 and butyric — stopped all fermentation only when 0.04 to 0.07 normal. 

 The most striking feature of Bial's work was a series of experiments 

 on the diminution of the antiseptic action of acids by the addition 

 of neutral salts whose action is to decrease the dissociation of the 

 acidic hydrogen. A solution of o.oi normal formic acid and 0.3 



