CONDITIONS FAVOUKING FERMENTATION. 13 



fermentative changes has of late years become familiar to many 

 workers, and is very generally recognized, more especially since 

 attention was prominently called to one side of the subject by 

 Pasteur in 1862*. He found that some neutral or slightly alka- 

 line boiled fluids would ferment more easily than otherwise similar 

 boiled acid fluids, tkough he made no observations as to the com- 

 parative influence of acids and alkalies upon unboiled fluids. 

 Taking into consideration a limited group of facts only, he en- 

 deavoured to account for them in a manner which, if not adverse 

 to, did not sufficiently appreciate, the wider point of view of 

 Grerhardt. 



Yet this wider point of view and the relative influence of acids 

 and alkalies may be demonstrated with the utmost ease, as I 

 pointed out in 1870 f- Thus, if two portions of an acid infusion 

 are exposed side by side at a temperature of 77° F. (25° C), fer- 

 mentation may be made to occur earlier, and to make more rapid 

 progress in either of them at will by the simple addition of a few 

 drops of liquor potassse ; and, on the other hand, if a neutral infu- 

 sion be taken and similarly divided into two portions placed, side 

 by side nnder the same conditions, fermentation may be retarded 

 and rendered slower in either of them at will, by the simple addi- 

 tion to it of a few drops of some strong acid. 



A neutral or faintly alkaline organic solution can in this way 

 be demonstrated, to possess a higher degree of fermentability 

 than an otherwise similar acid organic solution. It seems there- 

 fore obvious that the higher tendency to undergo change of these 

 fluids might be less easily stifled than the lower tendency pos- 

 sessed by acid infusions, and consequently that the changes ca- 

 pable of taking place in boiled neutral and acid infusions respec- 

 tively might be very different; the previous boiling, that is, 

 might not prevent the higher fermentability of neutral infusions 

 from still issuing in fermentation, though it might much more 

 frequently extinguish the lower fermentability of acid infusions. 



Numerous experiments by different observers have now demon- 

 strated the correctness of this inference. Boiled acid infusions, 

 guarded from contamination, mostly remain pure and barren if 

 kept at or below 77° P. (25° C), though some of the same infu- 

 sions similarly treated, except that they have been rendered neu- 

 tral by the addition of an alkali, will oftentimes become corrupt 



* Ann. de Chimie et de Physique, tome Ixiv. p. 58. 

 t Nature, July 14, p. 227. 



