The constituents of milk are first water, constituting from 65 to 90 per cent. Nitrogenous matter, consisting of the casein above described and a little albumen. Fat, sugar, and saline substances. The proportions of these vary so greatly in the milk from different animals of the same species, and in that from the same animal at different times that tabular statements of the percentage composition of the milk of different animals are very variable. I have five such tables before me, assembled for the purpose of supplying material for my readers, but they are so contradictory, though all by good chemists, that I am at a loss in making a choice. The following is Dr. Miller’s statement of the mean result of several analyses: +------------------------+-------+------+------+------+-------+-------+ | | Woman | Cow | Goat | Ass | Sheep | Bitch | +------------------------+-------+------+------+------+-------+-------+ | Water | 88·6 | 87·4 | 82·0 | 90·5 | 85·6 | 66·3 | | Fat | 2·6 | 4·0 | 4·5 | 1·4 | 4·5 | 14·8 | | Sugar and soluble salts| 4·9 | 5·0 | 4·5 | 6·4 | 4·2 | 2·9 | | Nitrogenous compounds }| | | | | | | | and insoluble salts }| 3·9 | 3·6 | 9·0 | 1·7 | 5·7 | 16·0 | +------------------------+-------+------+------+------+-------+-------+ The fat exists in the form of minute globules of oil suspended in the water. The rising of these to the surface forms the cream. When the milk is new it is slightly alkaline, and this assists in the admixture of the oil with the water, forming an emulsion which may be imitated by whipping olive or other similar oil in water. If the water is slightly alkaline the milky-looking emulsion is more easily obtained than in neutral water, still more so than when there is acid in the water. As milk becomes older lactic acid is formed; at first alkalinity is exchanged for neutrality, and afterwards the milk becomes acid. This assists in the separation of the cream. Butter is merely the oil globules aggregated by agitation or churning. The condition of the casein has been already described. The sugar of milk or ‘lactine’ is much less sweet than cane sugar.