88 BOARD OF AGRICULTURE. 



Is there not here a very substantial agreement ? How to make 

 such, is the inquiry next in order ; but before entering directly upon 

 it, some remarks will be offered regarding the nature and properties 

 of the material employed. 



Milk. — Milk is a secreted liquid, intended by nature as food for 

 the young of mammiferous animals, and to this end it is most ad- 

 mirably adapted. Like all the secretions of the animal body, milk 

 is a very compound substance ; and its composition varies a good 

 deal according to the circumstances attending its secretion. Ordi- 

 narily, the milk of the cow contains an amount varying from three 

 to five per cent, of each of the following substances : Oil, (or fatty 

 matter, or butter,) casein, (or curdy matter,) and sugar; it also 

 contains a very small proportion of salts, and from eighty-five to 

 ninety per cent, of water. 



To the naked eye milk appears to be an opaque uniform white 

 liquid, but such it is not in fact, and under a good microscope it is 

 readily seen to be a transparent liquid, bearing myriads of minute 

 globules diffused through it. These globules are the oil, or butter, 

 and give to the liquid its white, opaque appearance. Each of them 

 is enclosed in a little bag, or film, of curdy matter. After con- 

 tinued agitation, or by the action of heat, these little sacks burst 

 and liberate the fat, which then readily collects in a mass, and 

 when duly separated from the other substances, is butter. 



When milk is suffered to remain at rest, the oily particles slowly 

 separate, and being lighter than the liquid holding them, they rise 

 to the surface, and together with a portion of the cheesey matter, 

 form the unctuous clot or coat on the surface called cream. The 

 fatty matter does not wholly separate, as a portion remains in sus- 

 pension, and in proportion to the completeness of the separation, 

 the liquid assumes more or less of a bluish tint. 



Being only suspended, the separation of butter from milk is 

 mainly a mechanical process. Casein, on the contrary, is dissolved 

 in the water of the milk, and not merely suspended in it. By 

 what means it is thus held in solution is not known. Casein, under 

 ordinary circumstances, is insoluble in pure water. It will dissolve 

 in water in which a little soda is added. Freshly drawn milk not 

 unfrequcrftly contains a little free soda, and when this is the case 

 it is slightly alkaline ; and nearly all writers on the chemistry of 

 milk teach that it is by virtue of the presence of this free alkali 

 that the casin remains in solution. This theory is somewhat plans- 



