When we reflect on the importance of these small quantities of easily destroyed constituents in natural foods, we begin to appreciate the difficulty of securing a pure milk-supply which shall be at the same time a nourishing and a healthy one. The sterilizing of milk by heat before it is sold as an article of diet seems to be desirable in order to destroy the bovine tubercle-bacillus which may be there and the other injurious microbes due to the dirty conditions in which the cow is kept and the milkers keep themselves. The heating of the milk for some twenty minutes to a temperature below that of boiling water seems to be the best plan. For infants, meat-juice or beet-juice may then be added to the milk when used, and so "infantile scurvy" be avoided. Consumers (older children and adults) who are taking other foods do not need this additional precaution. Milk thus "Pasteurized" is the safest milk. But there is a very serious precaution to be observed in all cases. In such Pasteurized milk the lactic organism or ferment usually present is destroyed. Consequently the milk does not "go sour" by the growth of the lactic ferment. This is no advantage, but a serious danger. For the lactic "souring" of milk is not injurious, but, on the contrary, a safeguard. It actually prevents the growth in the milk of other really harmful and deadly germs. Thus when the lactic germ is not there, but killed by heat, these other deadly germs get their chance. A fly or other dirt-carrier brings to the sterilized milk "putrefactive" bacteria and such germs (terribly common) as those of "green" or infantile diarrhœa, not to mention others. If the milk had been unsterilized and gone sour by the growth of the lactic ferment, these more dangerous germs could not have flourished in the acid conditions produced by it. The danger of Pasteurized milk is that if kept more than a few hours at the ordinary temperature of a dwelling-room, and not carefully protected, it may be a very ready means of communicating infantile diarrhœa and other intestinal disease. It would therefore seem to be desirable to restore to the Pasteurized milk a small quantity of a pure culture of lactic germs. This could be easily done. The milk would have had its tubercle-bacilli and others removed by heat, and then, after cooling, it would receive a very few lactic germs as a protective in case it should be kept by the consumer long enough to get infected by the bacteria of intestinal disease. It is imperative that good, nourishing milk, free from germs of tubercle and of diarrhœa, shall be accessible to the millions in this country who cannot afford to pay eightpence a quart for it. It is a difficult demand to meet. What is said above explains the difficulty, and suggests an attempt to overcome it. CHAPTER XXXII CHRISTMAS TREES AND OTHER PINE TREES