CONDITIONS FAVOUKINa FEEMENTATION. 43 



dity which will be brought about in the stock of urine by expo- 

 sure to the temperature of 212° F. for a definite time and to that 

 of the incubator for a given number of days (though different 

 urines vary somewhat in their rate of change), there is the diffi- 

 culty before alluded to, that the urine in this altered state is pro- 

 bably less apt to be acted upon favourably by potash in any pro- 

 portion. Again, the most suitable proportion of potash to urine 

 where the latter is in this condition may not be similar to that 

 for recently boiled urine ; and the question as to what propor- 

 tion might be more suitable could only be determined with diffi- 

 culty and after numerous merely tentative trials. 



V. Interpretation of Experiments with Urine and Liquor Fotassce. 



The fermentability of an unboiled acid organic solution is, as I 

 have previously pointed out, lower in point of energy than that 

 of an otherwise similar solution which has been rendered neutral 

 or faintly alkaline*. This is an easily verifiable fact. 



It was first pointed out by Pasteur that the same kind of diffe- 

 rence was often encountered on the part of boiled infusions — that 

 is to say, that an acid infusion which had been boiled would have 

 its fermentability extinguished, though an otherwise similar neu- 

 tralized infusion would ferment even after it had been boiled. 



The higher tendency to ferment in the unboiled neutral infu- 

 sion makes it not difficult to understand, and might have prepared 

 us for Pasteur's announcement that this tendency is not extin- 

 guished by the same degree of heat as that which suffices to arrest 

 fermentation in an otherwise similar acid infusion. 



So far there is no room for dispute : I have mentioned only 

 simple facts which any careful experimenter can easily verify. 



But when we come to the question of the interpretation of 

 the facts, difficulties arise. Pasteur, believing that fermentations 

 are chemical processes only capable of being initiated by living 

 units (and in the cases to which we are referring by units which 

 are independent living organisms), declares that the different be- 

 haviour on the part of these boiled infusions is due to the fact 

 that all ferment-organisms and their germs are killed in the boiled 

 acid fluids, whilst they or their germs are able to survive in the 

 boiled neutral fluids. No other interpretation seemed to him 

 compatible with the truth of the " germ theory." Tet it should 



* See p. 13. 



