798 
Th,e Fermentations of Milk. 
their ascent to the surface. The liquid state of the fat in the 
globules is simply due to their isolation — a phenomenon familiar to 
physicists under the name of superfusion — and hence, as soon as 
they have been shaken into coalescence by churning, the fat solidifies 
because the temperature of the dairy is much below its true melting 
point. 
Most complicated, most mysterious, and most liable to change 
are the albuminoids of the milk, of which the best known are casein 
and a smaller quantity of soluble albumin, though others kre said 
to be present by various observers. Even “ separated ” milk has by 
no means lost all its opacity, though it has lost nearly all the fat 
globules to which that opacity is usually ascribed. .The -residual 
opacity is by some attributed to the small amount of phosphate of 
lime present, by others to the condition of some of the casein. 
Some of this substance is certainly not in the state of true solu- 
tion, since it is left behind on filtering the milk through a .filter of 
unglazed porcelain ; but -whether it is present as minute particles, or 
as a continuous gum or paste— like laundress’s starch, — is a moot 
point. The clear liquid filtering through the porcelain contains 
that portion of the casein which was in tme solution, together with 
the soluble albumin, which differs little from the serum albumin of 
blood. 
Enough has been said to illustrate the eminently complex nature 
of milk. But, besides the liability of its ingredients to purely 
chemical changes, they are precisely of the class best suited to 
undergo fermentative change, whilst in the albuminoids and mineral 
salts of the milk are found the most suitable nourishment ' for 
microbes of almost all descriptions, — in other words, for the organ- 
isms which modern science has recognised as the active agents 
in exciting and carrying on that class of chemical changes to which 
the name of fermentations has been given, on account of their 
general resemblance to the well-known fermentation of sugar into 
alcohol and carbonic acid by the agency of yeast. 
The first and all-important point, which has been made more and 
more clear as knowledge increased, is that milk drawn from the 
cow without contamination from outside may be kept indefinitely 
without further change ; in other words, all the known changes to 
which fresh milk is subject are due directly or indirectly to the 
action of microbes which gain access to it after it has been with- 
drawn from the udder. 
If the hands of the milker and the teats of the cow be carefully 
cleansed with acetic acid or other antiseptic, and the milk be drawn 
direct into sterilised glass vessels which are protected from contact 
with unfiltered air by cotton-wool plugs, no other precaution is 
requisite to prevent milk not only from turning sour but also from 
undergoing any other change. The first successful attempts to 
obtain sterile or keeping milk in this way were made by inserting a 
sterilised tube direct into the milk duct, but this was soon proved 
not to be necessary, and many patents have been taken out for 
obtaining sterile milk direct from the cow with a view to supplying 
