CONDITIONS FATOURING FERMENTATION. 



41 



condition of stability very similar to that which is possessed by a 

 mere mineral solution of ammonic tartrate with sodic phosphate ; 

 that is' to say, it invariably ferments when it is brought into con- 

 tact with living Bacteria, but not under the influence of the finer 

 atmospheric dust. It requires either living Bacteria (which would 

 appear to be scarce in the atmosphere) or else the chance advent 

 of some larger fragment of organic debris possibly containing 

 living Bacteria-germs in its substance or on its surface *. 



(z) Now we come to the third unknown term — that is, the 

 nature of the influence of potash upon the boiled acid fluid after 

 the probation-period. One thing seems quite clear, viz. that the 

 fertilizing action of such an amount of liquor potassae as it would 

 be suitable to add to a stock of urine immediately after it has been 

 boiled, does not repeat itself when this same amount of liquor 

 potussae is added to a similar stock of urine which has been kept 

 in a Warm place for a fortnight. One reason for this also is now 

 quite plain. Whatever other changes the urine may have under- 

 gone during the interval, it is obvious that it would have dimi- 

 nished in acidity, and, consequently, that the liquor potassae would 

 have been added in excess — a condition which antecedent experi- 

 ence had shown to be invariably attended by negative results. 



When therefore we find Dr. Koberts and Prof. Tyndall begin 

 with putting too much liquor potassae into their tubes, when 

 they adopted a wasteful method of heating, which would most 

 notably diminish the acidity of the urine, and when they finally 

 kept it in a warm place for a fortnight, and thus still further di- 

 minished its acidity, it was only to be expected that such fluids 

 should have invariably remained barren. The liquor potassae was 

 altogether wrongly proportioned to the acidity of the urine with 

 which it was ultimately allowed to mingle. The fallacies beset- 

 ting the supposed superior method to which they had resort, and 

 the one-si4edness of the reasoning which dictated and permitted 

 its adoption, thus become plain. 



But f /en if this difficulty as to the adjustment of the proper 

 quantity of liquor potassae to be added to a measured stock of 

 urine of known acidity, after a probation-period of so many days 

 at a given temperature, and after a given period of exposure to a 



* Proceed, of the Eoyal Soc. 1873 (No. 145), toI. xxi. p. 325. 



