178 
P0PULAE SCIENCE EEYIEW. 
turned upon the question whether country or town milk i^, 
or ought to be, the better of the two, and as considerable 
differences of opinion appear to exist on this question, it may 
not be amiss to offer a few remarks on it, after having placed 
in the hands of the reader the materials from which he may 
safely draw his own conclusions. The question in dispute does 
not so much depend on mere opinions as on facts, which can 
be readily ascertained by any one who will take the trouble to 
investigate carefully the various conditions which affect more 
or less appreciably the quality of milk. 
Good milk is a whitish liquid, of an agreeable sweetish 
taste, and faint but pleasant odour. It is essentially an 
emulsion of fatty particles in a solution of casein and milk- 
sugar. The fatty matter, however, is not contained in milk 
in a free condition, but enclosed in little cells consisting of 
casein, a substance which exists also in a state of solution in 
milk, and is precipitated spontaneously when milk gets sour ; 
in other words, the fat or butter occurs in milk encased in 
curd. Viewed under the microscope, milk appears as a trans- 
parent fluid full of small round or egg-shaped bodies, the so- 
called milk-globules. When milk is left undisturbed for 
some time these milk-globules rise to the surface, and may be 
removed in a great measure in the shape of cream. 
The remaining skimmed milk has a bluer colour and is 
more transparent than new milk, containing its full share of 
milk- globules, or cream, or butter globules, as they may be 
called with quite as much propriety. 
However long milk may be left at repose, it is not possible 
to skim off all the milk-globules, and hence the skimmed milk 
always contains some cream, which renders it more or less 
opaque. Were it possible to remove the cream-globules 
altogether, we should obtain a perfectly clear, watery liquor. 
On adding rennet or an acid to milk, curd separates, to 
which chemists give the name of casein, from its forming 
cheese ; and when the whey of milk, from which the curd and 
butter have been completely removed, is evaporated to 
dryness, a colourless, crystalline, sweet substance is obtained, 
which is known by the name of sugar of milk. 
When the curd is removed from milk by rennet, -and the 
clear whey is heated to the boiling point of water, a substance 
identical with white of eggs or albumen separates in white 
flakes. Milk dried and finally burned in the air leaves behind 
a quantity of ash, which is rich in phosphate of lime or bone- 
earth and alkaline salts — constituents largely required for the 
formation of bone and blood in the young animal. 
The curd and albumen of milk contain 15 J per cent, of 
nitrogen in round numbers, and in other respects resemble 
