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exceedingly difficult, if not impossible. Particularly is this so when
it is realised that all milk coming into Lambeth is bulked; not only
is the milk of cows from one farm mixed, but also the milk from
several producers. In consequence, seeing how widely spread is the
infection among the milch cows in the country generally, it is
comparatively rare to obtain a sample of milk from a large consignment
which is free from tubercle bacilli, the milk from one tuberculous
cow infecting all milk with which it is subsequently mixed.
There can be little surprise, therefore, at the pronouncement in
favour of pasteurisation in the latest report of the Chief Medical
Officer to the Ministry of Health.
The general bacteriological examination of milk, the second need
expressed in the Minister's letter, raises an entirely different question.
It is not a practical possibility to examine milk with a view to
isolating the widely varied pathogenic organisms with which it
may be infected other than the tubercle bacillus, so that a total
count (a) of all organisms, whether harmful or harmless, and the
count (b) of the number of bacillus coli, made according to the
methods laid down in the Ministry of Health Memorandum
139/Foods, are the two criteria upon which the degree of cleanliness
of the milk is based.
Quite apart from natural criticisms of the value of such a count as
(a), there are technical difficulties. It is impossible to get a fair
sample of the contents of a churn of milk, even after vigorous
stirring, as experiments have proved that a different count is
obtained from samples taken from different levels in the churn.
The introduction of a plunger in itself may also add to the
contamination of the milk. Even if what is considered a fair
sample be examined, different counts will be obtained if the media
upon which the microbes are grown, are made up according to
the same formula, but the constituents are manufactured by
different firms. One firm's peptone, for example, will give one count
and another firm's peptone another. Not only so, but no two
counts on the same media made from the same sample give the
same result. With regard to (b) the bacillus coli count appears to
be the one likely to give the surest criterion of contamination,
because it is much more accurate and seeing that the ultimate
source of the organisms is the intestine of some living creature,
some indication of the possibility of the presence of pathogenic
organisms of gastro intestinal diseases can be obtained.
There being no legal standard of the bacterial content of other
than graded milks, the most contaminated milk, namely, ordinary