The observations of numerous workers agree in showing that pasteurization has the following effects. About 5 per cent of the lactalbumin is coagulated;—the coagulation time by rennin is lenge thened, but the casein clot formed consists' of finer particles and is of a more open texture; there is a diminution in the soluble calcium and phosphate, estimated variously by different workers, but probably of the order of 5 per cent; there may some 1065 of iodine through volat tion; there is* some destruction, at pr ut unmeasured but apparently small, of min B; and there is some diminution in the vitamin C content, depending largely on/ the amount of previous exposure to ight and on the presence of copper int the pasteurizing plant. Information on the effect of pasteurization on vitamin D is still deficient, but considering that vitamin D s even more resistant to heat and oxidation than vitamin A, it improbable that any deleterious effect occurs.
As against these positive changes may be set a number of negative findings. Thus it is found from feeding experiments on rats and calves that the biological value of the pro-reins is unaltered, that there is no detectable change in the availability of calcium or phosphorus, that there >|is no loss of vitamin A, and that the total energy value of the milk remains unaltered. Furthermore, recent carefully- designed experiments on calves in which alternate animals were fed for 8-12 weeks on raw and ed milk from the same source, have failed to show any significant difference in growth between the two groups of animals, In each experiment the average per-[centage weight increase was slightly higher in the group of animals receiving the pasteurized supply, but the differences were such as might easily have occurred by chance variation alone.
Cow's v. Human Milk In assessing these results in terms of human nutrition it must be remembered that, though cows' milk may be a perfect food for calves, it is not a perfect food for infants. It differs both qualitatively aha quantitatively from human milk, and it is deficient in iron, copper, vitamin C, and often in vitamin D. The di ferences between raw and pasteurized cows' milk are very much less than those between cows' milk and human milk. Deductions, therefore, from animal experiments to man must be made with great caution, Unfortunately, there is a dearth of direct observations to determine the comparative nutritive value of raw and pasteurized milk for infants and children. The only experiment of any size that is on record yielded results which failed to show any significant differences between the two classes of milk. Pending the publication of further observations of this type, we must conclude on the basis of all the available evidence that the nutritive changes produced by pasteurization appear to be comparatively slight, and are such as can readily be made good by suitable supplements to the dietary.
Milk-borne diseases Turning now to the hygienic aspect of pasteurization, we have at our disposal well-documented evidence to show the danger of drinking ordinary raw milk and the protection afforded by adequate pasteurization against milk-borne disease. It is calculated that in 1931 there were 2,600 deaths in Great Britain from tuberculosis of bovine origin and more than 6,000 fresh cases of the disease. Since then our knowledge of the part played by the bovine tubercle bacillus in causing pulmonary tuberculosis has considerably expanded, and there is no doubt that if this calculation were to be made afresh the figures would have to be increased rather than diminished, Undulant fever is a less important disease, but something like 400 cases yearly appear to arise in Great Britain, mainly from milk-borne infection. Of epidemic diseases records are available of the occurrence in Great Britain during the years 1912- 35 of at least 103 milk-borne outbreaks of scarlet fever, septic sore throat, diphtheria, typhoid fever, paratyphoid fever, dysentery and gostro-enterists affecting over 11,000 persons. These figures take no account of epidemic diarrhea, in the causation of which milk almost certainly plays a considerable part. Our knowledge of sporadic milk-borne disease, apart from tuberculosis and undulant fever, is very deficient, since milk is rarely suspected as a vehicle of infection unless large numbers of cases occur in a short interval of time over a limited area, but as further information accumulates on this subject, it seems likely that.the case against raw milk will have to be weighted still more heavily.
Text read from the printed page and cleaned; old type leaves the occasional error.