Excitement, or fretfulness; change of locality, or to a different herd, with new companions; separation from her calf; periodical heat; annoyance from flies, or worry from dogs; exposure to storms, severe cold, or an oppressive sun, and many similar causes, diminish the quantity of milk and butter; but some of these may reasonably be expected to increase the proportion of its casein. Dr. Playfair found that the quantity of butter in the evening milk, after the cow had been at pasture all day, was 3.7 per cent., while the casein was 5.4; after lying quietly all night, the milk from the same cow, on the following morning, contained 5.6 per cent. of butter, and only 3.9 of casein. In stabling the cow, the butter was invariably in greater proportion than when allowed to ramble in the pasture; and the casein, with a single exception, was equally diminished. [Illustration: Fig. 17. Lactometer, or Cream Guage.] Fig. 17, is a number of glass tubes of equal size, set in a frame called a _lactometer_ or _cream guage_. If milk from different cows be set in these, the depth of the cream will indicate their comparative richness. Cream. If milk be immediately set away in shallow vessels, after being taken from the cow, the cream rises to the surface, carrying with it most of the butter contained in the milk, and much of its casein also. Hence, the great nutritive properties of buttermilk, which retains the casein in very large proportions, much of it being rejected by the butter in its separation from the cream. A temperature below 34°, will prevent the cream from rising in any considerable quantity, and preserve the milk unaltered for some weeks. Coagulating the milk from any cause, will equally prevent the separation of the cream. The elevation of temperature within certain limits, hastens the separation. Thus, at 50°, the cream will mostly have risen in 36 hours; at 55°, in 24; at 68°, in 18 or 20; and at 77°, in 10 or 12 hours. Heating the milk near the boiling point, and then setting it away and allowing it to remain undisturbed, will soon cause the cream to rise. In the celebrated Orange dairy, near Baltimore, Md., this system was practised, by which, not only most of the cream was secured for butter, but in consequence of its rapid separation, the skimmed milk was sent to market within a few hours after being drawn; and the scalding imparted to it an agreeable flavor and apparent richness, which it did not really possess.