CONCLUDING EXAMINATION 205 
Mitk.—lIf heated to 230° F. (110° C.) for three- 
quarters of an hour or more, milk is found to be 
distinctly discoloured by the process. It is then of 
a light fawn-colour. A briefer exposure, however, 
to this temperature does not appreciably affect its 
colour. 
After it has stood in the incubator for twenty-four 
hours or so, a cream-like layer is found at the 
surface, the upper stratum of which is yellow and 
dry, though it is dotted here and there with globules 
of fluid oil. At this stage the fluid below is still 
white and opaque ; but where fermentation ensues, 
it gradually becomes more and more whey-like, and 
at last it may assume the appearance of mere dirty 
water. If left for a long time, the fluid may 
undergo other changes, and after a time become 
much discoloured. If the milk has been heated to 
230 F. for as long as 30 minutes or more, it may 
remain many days in the incubator at 122° F. before 
it shows any sign of change. 
When a specimen of superheated milk has fer- 
mented and become most notably altered in appear- 
ance, it still retains the simple odour of boiled milk. 
Its reaction, however, has changed, since it is always 
found to have become more or less acid. 
When I first examined such a specimen of milk 
under the microscope, I was puzzled at not being 
able to discover any distinct or definite organisms 
amidst the milk-globules. It is true there was a 
teeming myriad of swarming particles everywhere, 
too minute to be individually recognised, and 
recognisable principally by their aggregate motions. 

