144 THE EVOLUTION OF LIFE 

flame, may only have come into contact with steam 
at 212° F.), into continuous contact with the heated 
fluid itself.1 
After the urine in the boiled retort has become 
cool, the liquor potassz is allowed to mix therewith. 
This is easily brought about by shaking the retort 
or flask so as to jerk the bent capillary extremity of 
the liquor-potasseze tube against its internal surface. 
The neck of the previously closed tube is thus 
broken off, and the liquor-potassz itself, owing to 
the comparative vacuum within the experimental 
vessel, is forced out and mingles with the sterilised 
acid urine. 
If six to ten vessels have been prepared in this 
way, charged from the same stock of urine, some one 
or two of them may be selected for “control” ex- 
periments. In these the liquor-potasse tubes are 
not broken, while in all the others they are; so that 
when subsequently placed in the incubator together 
at a temperature of 122° F., the two sets of retorts 
constitute crucial experiments capable of testing the 
influence of liquor-potassze upon the sterilised urine. 
What I have found to happen almost uniformly 
in about two hundred of such experiments is this: 
If suitable fluids are dealt with—that is, specimens 
of fresh urine whose acidity before boiling does not 
require less than 8 minims of liquor potassz per 
ounce for neutralisation, and which do not deposit 
phosphates on boiling—the urine in the control ex- 
1The whole of the internal surface of the liquor-potassz tube is 
similarly exposed to the influence of its heated and caustic fluid during 
these different modes of heating. 
