COKDITIONS FAVOTJEING rERMENTATION. 9 



after this event. This is a distinction of considerable importance. 

 If we take a urine whose acidity equals 10-15 minims of liquor po- 

 tassae per ounce, if we boil it and subsequently keep it for a long 

 time in the incubator at 122° ¥., it remains barren ; and yet on 

 opening the vessel and testing its acidity we may lind that this 

 has been reduced to five, four, or two minims per ounce ; it may 

 even be neutral*. The occurrence or not of fermentation in any 

 given specimen of urine at 122° F. is, therefore, not a question 

 of its less or greater acidity at some period subsequent to the 

 process of boiling, but of its degree of acidity at the time of 

 ebullition itself. Effects are produced by the heat plus the large 

 amount of acid, which are not produced by the heat and a smaller 

 amount of acid ; and these effects may be merely germicidalj or 

 they may be more purely chemical in their nature f. 



III. Oxygen as a Promoter of Fermentation. 



Early in the present century Gay-Lussac assigned to oxygen an 

 all-important role in the initiation of fermentative changes. He 

 and his followers regarded the oxygen of the atmosphere as the 

 " primum movens " in all fermentations — a doctrine which, though 

 it is in the present day generally admitted to be too exclusive, 

 was for a long time almost universally accepted. But even now no 

 one questions the fact that oxygen acts in common with other 

 agencies as a powerful inciter of fermentation and putrefaction. 



I freely admit this latter proposition, although I have brought 

 forward some evidence tending to show that certain fermentative 

 processes may be initiated just as freely (or rather more so) in 

 closed vessels from which almost the whole of the air has been ex- 

 pelled by boiling, as in others in which atmospheric air, and con- 

 sequently oxygen, is present in much larger quantity J. 



* See further on, at page 47, footnote *. 



t The fact itself is shown by the different influence of potash upon an acid 

 urine according as it is added before or after the process of boiling. A urine 

 of twelve minims' acidity to which sis minims per ounce of liquor potassce has 

 been added before boiling, will ferment freely under the influence of 122° F. ; 

 but if this same urine had been boiled in its fully acid state, and the six minims 

 per ounce of liquor potassse were added afterwards, no such result would follow ; 

 or if it ever did ferment, it would be only rarely and after an interval of many 

 days. This is an anticipation of a subject to be considered further on, but which 

 it is useful to note here. 



\ ' Beginnings of Life,' Appendix 0, expts. viii., ix., xiv., xv., xviii., xx., xxvi., 

 XXX., xxxiii., and xxxvi. 



