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disease. Immunisation is not to-day of any importance in the control of tuberculosis (paragraphs 29-34).
(6) Cattle are probably infected with contagious abortion in as great numbers as with tuberculosis. The disease does not cause death, but is responsible for very serious loss to farmers by causing the loss Living of calves and of milk and by rendering animals sterile. animals may be shown by a blood agglutination test to be infected. Herds may achieve a comparatively high degree of immunity from this disease, either naturally or as a result of vaccination. Vaccination can usefully be adopted if the total eradication of disease by segregation is impracticable; but, if a living virus is used, vaccination should only be adopted in dealing with heavily infected herds (paragraphs 35-40).
(7) The incidence of Johne's disease varies greatly throughout the country. In some districts it is increasing and is causing considerable anxiety. It results in emaciation and, finally, in death. There is not yet a reliable agent for the diagnosis of the disease before clinical symptoms appear. There is no known cure (paragraphs 41–43).
(8) Thirty per cent. of the milking cattle in this country are probably infected with mastitis other than tubercular mastitis. Chronic streptococcal mastitis is responsible for 90 per cent. of the cases. It gradually reduces the milk-producing powers of the infected animal (paragraphs 44–48).
Diseases in man associated with cattle diseases.
(9) The diseases of dairy cattle which are dangerous to man are bovine tuberculosis, contagious abortion, which is responsible for undulant fever, and those forms of mastitis which may cause the epidemic diseases that are associated with streptococcal infection. Milk originally pure may convey disease as a result of subsequent Infection (paragraph 49).
(10) Bovine tuberculosis is responsible for over 2,500 deaths annually among the human population in Great Britain, and for a still greater amount of serious illness. Most bovine tuberculosis in human beings is attributable to milk. At least 5 cows in every 1,000 yield milk infected with tuberculosis. As the result of the mixing of such milk with pure milk, over 5 per cent. of samples from individual herds are infected. A very much larger percentage of the milk conveyed in large containers is infected. The degree of infection of milk when retailed is affected by the extent to which it has been treated. In London, an Investigation by the London County Council showed that 3.2 per cent. of samples of milk retailed are infected. In the four large cities of Scotland the corresponding percentage has been estimated at 5-26. The bulking of milk is more likely to increase than to decrease the risk of infection to man (paragraphs 50-57).
(11) Undulant fever, the disease associated with contagious abortion in cattle, is very rarely reported in Great Britain, though possibly the disease often passes unrecognised. Though it is
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Important that farmers should not relax their efforts to reduce the extent to which their herds are infected with abortion, it is doubtful whether any measures that are practicable can be taken to reduce the incidence of undulant fever in man (paragraphs 58, 59).
(12) Approximately 100 outbreaks of epidemio disease, attributable either to mastitis among cattle or to subsequent infection of milk by those handling it, have been recorded in this country since 1903. The most important outbreak occurred at Hove in 1929, when 1,000 families were affected and 65 deaths occurred. The most common epidemic diseases carried by milk are scarlet fever, enteric fever, diphtheria, paratyphoid and septic sore throat. The reported outbreaks have not contributed much to the total incidence of the diseases in question, but the possibility that infection through milk is more extensive than appears from the outbreaks reported cannot be ruled out. The organisms responsible for these infections multiply rapidly in milk, and the bulking of milk contributes enormously to the chances of infection (paragraphs 60–62).
Milk in human diet and the effects of pasteurisation on it. (13) Milk holds a unique position amongst the foods of animal origin, as it contains the three proximate principles of a diet, protein, fat, and carbohydrate, in addition to an adequate supply of inorganic constituents in such proportions as to be peculiarly adapted for the period of active growth. Cow's milk is not the ideal nutriment for the human infant, as milk secreted by the female of any species is peculiarly fitted for the rate of growth of the young of that species. Although mother's milk is unquestionably the best for the infant, cow's milk can be counted as a good substitute, provided that it is pure (paragraphs 63–71).
(14) The evidence available to-day leaves the conviction that any recognisable changes of quality induced in milk by pasteurisation rightly conducted are too small to outweigh the great advantage inherent in the protection from infection which the treatment secures and in the public confidence it inspires. It is sometimes suggested that there may be subtle changes not revealed in the state of present knowledge, but policy should not be influenced by vague possibilities which established evidence makes improbable (paragraphs 72–98).
(15) Children reared on milk should be supplied with fruit juice, whether the milk is raw or pasteurised. The custom seems now to have become common, though not universal. Through the winter, it is also highly desirable that cod liver oil should be administered in small doses to children under twelve months reared on cow's milk (paragraphs 99-101).
Administrative measures in force in regard to cattle diseases and the milk supply.
(16) The tuberculosis order of 1925 requires that animals yielding tuberculous milk or showing clinical signs of tuberculosis should be
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