London's Pulse: Medical Officer of Health reports 1848-1972
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Hints from the Health Department. Leaflet from the archive of the Society of Medical Officers of Health. Credit: Wellcome Collection, London
Kensington 1930
[Report of the Medical Officer of Health for Kensington Borough]
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During the year, four samples of "Certified Milk," one of "Grade A (Tuberculin Tested) Milk," and seven of "Pasteurised Milk" were taken for the purpose of ascertaining whether they complied with the bacteriological standards laid down in the Milk (Special Designations) Order, which are as follow :—
| Special class of milk. | Maximum number of bacteria permitted per c.c. | Standard for bacillus coli. |
|---|---|---|
| " Certified Milk " | 30,000 | Must not be found in one- tenth c.c. |
| " Grade A. (Tuberculin Tested) Milk " | 200,000 | Must not be found in one-hundredth c.c. |
| " Pasteurised Milk " | 100,000 | No standard provided. |
The results of the examinations are shown in the following tables:—
| Sample collected on. | Bacteria per 1 c.c. | Coli per l/10th c.c |
|---|---|---|
| 8th April | 5,300 | Nil. |
| 15th July | 6,100 | ,, |
| 30th September | 1,300 | ,, |
| 16th December | 880 | ,, |
| Coli oer 1/lOOth c.c. | ||
| 12th March | 10,400 | Nil. |
| 4th February | 14,700 | |
| 12th February | 36,000 | |
| 3rd April | 17,800 | |
| 3rd April | 15,200 | |
| 2nd September | 19,300 | |
| 2nd September | 18,200 | |
| 16th September | 2,830 | |
All the samples of graded milks proved to be well within the bacteriological standards prescribed
by the Order and indeed may be classed as very pure milks.
Investigations into Methods of Sampling Milk for Bacteriological Examination.—The Ministry
of Health in February, 1929, issued a memorandum (Memo. 139/Foods) dealing with the
bacteriological tests for graded milk and sampling of milk.
These suggestions, however, dealt chiefly with the precautions to be observed during the
transit of samples to the laboratory and contained no rules for the guidance of sampling officers
in taking samples from bulk milk. Thus the method of sampling to be adopted within their own
area has been left to the discretion of medical officers of health and sampling officers.
Experience in Kensington led to doubt as to whether the sampling instruments in common
use by local authorities are really suitable for taking samples under the Ministry of Health's
Regulations, and during 1930 an investigation was made into the question.
The investigation was carried out by Dr. T. S. Keith, the Borough Bacteriologist and
Mr. H. W. Walters, the Council's food inspector, and as a result of a number of experiments
they arrived at the conclusion that the present methods of taking samples give uneven and
unreliable results from the point of view of bacteriological examination.
The sampling instruments were those suggested by Delépine, or modifications thereof, none
of which exceeds nine inches in length. These instruments are unsuitable for thoroughly mixing
the milk in a churn and any sample collected with the aid of them would be taken from a depth
in the churn not exceeding 6 inches from the surface of the milk.
Thus it will be appreciated that a sample taken in the manner indicated could only be a fair
one if the bacteria in the milk were distributed evenly throughout the entire bulk. In order to
ascertain if the bacteria were so distributed the following experiments were carried out.
By means of four, and later three pipettes joined together, samples of milk were collected
simultaneously from four (or three) different levels in a churn. When four samples were collected
they were taken from the bottom of the churn, 6 inches up, 12 inches up and 18 inches up and
when only three were collected they were taken from the bottom, 9 inches up and 18 inches up.
The results obtained during these experiments showed that the variation in the bacteria
count was considerable and that the higher the level in the churn from which the sample was
taken the larger the count.