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the milk is raised, and the time during which it is exposed to the
high temperature. On this subject I cannot do better than quote the
following extract from a paper contributed by Dr. Macfadyen to the
Transactions of the British Institute of Public Health, which sums
up our present knowledge with regard to the sterilization of milk:—
"Whilst the Pasteurising process weeds out the non-sporing lactic
bacteria from milk, a temperature of 100° c. for one hour is necessary to
destroy the butyric acid organisms, and even when this has been accomplished
the milk cannot be called sterile. There still remain the spores of organisms
belonging to the group of the hay bacilli which are able to resist a temperature
of 100° c. for three to six hours. A sterilization of milk to be absolute would
consequently require six hours heating at boiling point, or at an exposure for a
shorter period to steam under pressure by means of the autoclave. These
very resistant forms produce little visible change in the milk, but its taste
becomes bitter and pungent. Certain members of this group have marked
toxic properties, causing fatal diarrhoea in young dogs and cats.
It is well known, domestic sterilization of milk is very unreliable,
the temperature not often being raked to the boiling point, and the
period of exposure to this being very variable. Under these circumstances,
domestic boiling of milk, while useful, cannot be regarded as
an absolute safeguard against the transmission of disease by this
means.
I have now to give in detail the result of my investigations under
the following heads:—
1. Bacteriological examination of milk samples.
2. Replies of Medical Practitioners to circular letter.
3. House-to-house enquiry in special areas.
1. The following is the report of the director of the Jenner
Institute, to whom the suspected milk samples were submitted for
examination.