Inasmuch as the milk furnished to consumers in large cities in summer contains at the time of delivery an immense number of miscellaneous bacteria, this procedure may not fully meet the requirements during hot weather, not only because such milk will not remain sweet for twenty-four hours unless kept in a good refrigerator, but also because the bacteria not destroyed by the heating may at times produce digestive disturbances in the very young. Under such circumstances it is best to keep the bottles in the water until it boils or to use one of the many steamers now on the market. After the bottles have been kept at the boiling point for three to five minutes (or longer if they are large) they should be cooled as promptly as possible and kept in a refrigerator until used. The simplest plan is to take a tin pail and invert a perforated tin pie-plate in the bottom, or have made for it a removable false bottom perforated with holes and having legs half an inch high to allow circulation of the water. The milk-bottle is set on this false bottom, and sufficient water is put into the pail to reach the level of the surface of the milk in the bottle. A hole may be punched in the cover of the pail, a cork inserted, and a chemical thermometer put through the cork, so that the bulb dips into the water. The temperature can thus be watched without removing the cover. If preferred, an ordinary dairy thermometer[21] may be used and the temperature read from time to time by removing the lid. This is very easily arranged, and is just as satisfactory as the patented apparatus sold for the same purpose. Any other simple method of procedure will give the same result. [21] Before using the dairy thermometer it is best to have it tested, as it may be unreliable in the upper parts of the scale. _Average Content of Fat in American Milk._--From the thousands of analyses of American milks that have been made it appears that the average content of fat therein is about 3.90 percent. Of the different breeds of cows the Holsteins produce milk with the least content of fat and the Jerseys with the greatest. It is not unusual to find in the milk of a Jersey cow a content of 6 or 7 percent of fat. =Comparison of Cow’s Milk with Other Varieties.=--Human milk differs from milk chiefly in having a much lower content of casein and a higher content of milk sugar. Goat’s milk has a higher content of casein than milk, somewhat higher content of fat, and slightly less sugar. Ewe’s milk is very rich both in protein and fat. Mare’s has a low casein and fat content and is exceptionally rich in sugar. Ass’s milk has less casein and protein than milk but more sugar.