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The Graded Milks are classified as (i) Certified, (ii) Grade A
(Tuberculin Tested), (iii) Grade A (Pasteurised), (iv) Grade A, and
(v) Pasteurised. The first two may not be treated with heat at
any stage before reaching the consumer, while both forms of
pasteurised milk may only be treated with heat once and then by the
holder process, the milk being held at a temperature not less than
145° F. for half an hour.
The maximum number of micro-organisms each grade may
contain is laid down in the Order. In contrast ungraded milk may
contain any number of organisms as it has no bacterial qualifications
whatever.
The pathogenic or disease-producing organisms which may be
found in milk fall broadly into two main divisions, those from the
cow and those from outside sources of human origin introduced by
human agency in the processes of milking, transport and
marketing.
Organisms from the cow are principally the Bovine Tubercle
Bacillus, the Bacillus Abortus (Undulent Fever in man), and
streptococci and staphylococci from inflamed udders and teats
which may give rise to epidemic, sore throats, etc. Foot and
mouth disease is but rarely contracted by human beings from
infected milk. The principal disease direct from the cow is, of
course, the disease of bones and joints mainly occurring in children
and caused by the Bovine Tubercle Bacillus; the others are rarities
in comparison.
Disease-causing organisms of human origin introduced by human
agency are principally the streptococcus hsemolyticus, the cause of
scarlet fever or modified and variant forms of that disease, the
diphtheria bacillus, human tubercle bacillus, organisms causing
gastro-intestinal diseases such as the enteric group and the
bacillary dysenteries, and the gaertner, aertryche and salmonella
group which causes food poisoning.
All these disease organisms, whether bovine or human in origin,
are killed by the holder process of pasteurisation.
The letter from the Minister suggests that ordinary milk on sale
should be examined for the presence of tubercle bacilli. In actual
practice there is no short cut in this examination. The only
certain method known is by animal inoculation, and the absence of
tubercle bacilli in the milk cannot be accepted as definitely proved
in less than three weeks, the guinea pig not showing definite proof
in less time. When a positive result is obtained, useful action is
limited to tracing the infected cow, which, after such a period, is