202 THE EVOLUTION OF LIFE 
mentioned, and when it is heated to 230° F. (110° 
C.) or upwards, does not, as a rule, exhibit any very 
well-marked turbidity. Nevertheless the fluid may 
grow perceptibly clouded; and while it becomes 
appreciably lighter in colour, a flocculent precipitate 
gradually accumulates. In other cases we may have 
whitish tufts of organisms manifesting themselves, 
and visibly increasing in size, while the fluid around 
remains clear. Lastly, in the least satisfactory cases, 
we may have neither of the foregoing signs of 
change, but only a slow accumulation of a sedi- 
mentary matter, amongst which, in certain cases, 
organisms are to be found that are unquestionably 
living. Still, it is also true that deposits of mere 
amorphous and crystalline matter will generally 
accumulate after a time at the bottom of even a 
well-filtered hay-infusion, in cases in which no 
fermentation is initiated. Hence it is that this latter 
kind of change is unsatisfactory, and we need the 
microscope to tell us whether or not we really have 
to do with a ‘smouldering fermentation” in which 
a limited number of organisms are present. 
It will thus be seen that the fermentation is 
almost always less vigorous in these superheated 
hay-infusions than where they are merely boiled, 
and its modes of manifestation are almost exactly 
the same as for urine. I have, however, met with 
some exceptions to this. Thus, last summer fourteen 
specimens of a hay-infusion heated to 230° F. for 
five minutes, and subsequently exposed in the in- 
cubator to a temperature of 122° F., showed after 
twenty-four hours many Bacilli-tufts, which continued 

