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83
One hundred and fifty cubic centimetres (150 c.c.), equal to 5.28 ounces,
British, of each sample were submitted to examination in the following way,
All the solid particles in each sample of milk were collected as a deposit by
prolonged centrifugation in a Runne machine. The amount of sediment thus
collected was then estimated by bulk. Next, six "coverglass specimens" were
prepared from the sediment, and stained for microscopic examination. The
residue of the sediment was used for the biological test, being divided into two
equal portions, each of which was administered to a guinea-pig.
[The results in detail of the examination were set out in the Council's Minutes ]
I. The Condition of the Samples with respect to General Cleanliness.
In the first place it may be mentioned that, excepting sample 20, which was
heavily tinged with anatto, none of the samples presented any obvious
appearance of added colouring matter.
The amount of foreign dirt present in each sample was carefully estimated by
gauging the amount of sediment thrown down after a prolonged centrifugation
of the milk. The term "foreign dirt," it may be explained, is used as denoting
extraneous solid matter which has gained access to the milk after it has left the
cow, and not as including pus, which is presumably yielded by the cow with the
milk. In one or two of the samples, however, and notably in the case of sample
24, the estimated bulk of foreign dirt does include a relatively small quantity of
pus; but, generally speaking, the sediment on which the classification of these
samples is founded consisted of foreign dirt only. Sample 10, which was
heavily contaminated with pus, contained only a small quantity of foreign dirt.
This foreign dirt, under the conditions of the taking of these samples, may
obviously gain access to the milk either whilst still in the cowsheds, during
process of transit, during storage with the retailer, or in the process of delivery
to the consumer by the retailer. The methods of examination available will not,
as a rule, afford any reliable indication as to the particular stage at which the
bulk of the foreign dirt which may be present gained access to the milk.
An endeavour was made to classify the varying degrees of cleanliness or
dirtiness of these samples, according to an arbitrary figure scale, as follows:—
1.—Not more than three or four obvious particles of dirt in the
sediment thrown down from 150 cubic centimetres of the milk.
2.—Rather more dirt than indicated by "1," but still not sufficient to
form a coherent sediment.
3.—A small, but definite, coherent sediment of dirt particles.