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fluid.) "This sparseness of cells ,in a condensed milk is probably due to the fact that
they are in part got rid of in the sediment which is carried down during centrifugalisation
and adheres to the vessel. Moreover, differential counts on films from machine
skimmed brands, even when these are swarming with staphylococci, present no deviation
from those seen in good milks. Thus in seven samples the percentage of polynuclears
was 57, 62, 74.5, 64, 60, 60 and 68. It might be expected that the presence of actual
pus in the milk, or even the admixture of milk suffering from non-suppurative mastitis,
would raise the percentage of the polynuclears.
Experience has, however, shown in the case of fresh milks that too much reliance
must not be placed on this, because in a herd the milk of one or two affected cows
mingled with a hundred or more normal milks scarcely affects the cellular content of
the whole.
Conclusions as regards the Cells in Condensed Milk.
I have to admit that the studies of condensed milks which I have outlined above
have considerably modified my first opinions as to the nature of the cellular contents
of condensed milk. I no longer think that one should apply the term "pus" to a
sediment merely because it is rich in polynuclear cells, without a count of the actual
number of such cells per cubic millimetre of the milk and a careful consideration of
the associated microbes, and even here there may be fallacies which I shall consider
below. That the presence of such cells in very large numbers may indicate pus no one
will dispute, but it is not a matter to be settled without careful consideration.
The Bacteriology of Condensed Milks.
I have said that unsweetened and little condensed milks are necessarily sterilised ;
they have no bacteriology. One cannot find bacteria in them microscopically, since the
dead bodies of the original bacteria in the fresh milk appear to become disintegrated
and invisible. At most one may find a few badly stained ghosts.
In the case of sweetened condensed milks the case is very different. In the course
of these investigations I have examined 44 tins of such milk by ordinary bacteriological
methods, though in no case quantitatively. That is to say, I have made agar cultures
from a minute quantity of the sediment from each milk, about the same amount in each
case, being a very small drop from the end of a capillary pipette. The results are
roughly comparable, but only roughly.
In a preliminary investigation of this kind I deemed it unnecessary to attempt
quantitative estimations, though it may clearly be necessary to do so if any arbitrary
standard is to be set up.
In no single one of the 44 tins examined were living bacteria absent, and they were
usually present in considerable numbers. In the process of preparation the condensed
milk seems to be subjected to a temperature sufficient to destroy the bulk of the
contained bacteria, and when prepared the chemical nature of the product seems to
render it unfit for the life, or at least for the growth of most surviving bacteria. All
observers are agreed that the bacterial contents of condensed milk is greatly less than
that of fresh milk, and that even when the tin is opened its contents undergo
decomposition slowly. We have therefore to consider the survival chances of the