1876.] Physico-Chemical Theory of Fermentation, .^c. 151 



the generally received opinion that temperatures above 100° F. (38° C.) 

 were likely to impede rather than promote fermentation. 



In maintaining the experimental fluids at the high temperature aboA^e 

 named, the vessels containing them were placed in the hot-air chamber 

 of an incubator such as physiologists employ, to which one of the very 

 ingenious gas-regulators of Mr. F. J. Page had been fitted (see Journal of 

 the Chemical Society, January, 1876). In this way the fluids may be kept 

 at a known and practically constant temperature for an indefinite time. 



Liquor Potassce as a promoter of Fermentation in Boiled Urine. 



In the autumn of 1875 the author instituted some experiments to 

 ascertain whether the fermentability of boiled urine, like that of many 

 other fluids, could be increased by previously mixing with it a quantity 

 of liquor potassse sufiicient for its neutralization. 



The experiments answered this question in the affirmative. It was 

 found that urine to which the above-named amount of liquor potassse had 

 been added would constantly ferment and swarm mth organisms within 

 a few days after it had been boiled, though some of the same stock of 

 urine in the acid state (that is, without the addition of any alkali) would 

 when similarly treated in other respects remain barren. The fact of the 

 production of an increased fermentability in boiled urine by previous 

 neutralization was thus established. 



Eurther experiments vi^ere then instituted to throw light upon the 

 cause of such increased fermentability. It was desirable to ascertain 

 whether (1) it was due to survival of germs in the boiled neutralized 

 fluid, or (2) to the chemical influence of potash in initiating or helping 

 to initiate the molecular changes leading to fermentation in a fluid 

 devoid of germs or other living matter. 



The mode of testing the relative validity of these rival interpretations 

 seemed easy. It was only necessary to ascertain what the efl^ect would 

 be of adding boiled liquor potassse, in proper quantity, after the acid urine 

 had been rendered barren by boiling it, instead of adding it previous to 

 the process of ebullition. If fermentation occurred in the fluid thus 

 neutralized without extraneous contamination, the first interpretation 

 would obviously be negatived. 



This crucial experiment was at first tried with flasks plugged with 

 cotton-wool, the plug in each of them being penetrated by a closed glass 

 tube containing the measured amount of Hquor potassae. The tubes 

 having been dra^Ti out to a capillary portion at the lo^ er end, and bent 

 at an obtuse angle, they could be easily broken by slight downward pres- 

 sure against the bottom of the flask whenever it was desired to mix the 

 liquor potassse with the boiled urine. This apparatus was very similar 

 to that first made use of by Dr. William Eoberts in some experiments 

 with hay-infusion (Phil. Trans, vol. clxiv. p. 474), in which he obtained 

 o'[)posite results from those now about to be recorded with urine. The 



