1847.] Butter Churning. 171 



air is not necessary to the changes which attend it; yet, in ordi- 

 nary churning, it is probable that the presence of air does exer- 

 cise a real inHuence upon the process, modifying its rapidity and 

 the quality of the butter obtained. It is probable, also, that those 

 forms of churn which admit the air to the most intimate and re- 

 newed contact with the milk, may also facilitate the changes by 

 which churning is attended, and, as I have explained in the pre- 

 ceding article, may cause the same milk to yield a harder butter 

 than would otherwise have been obtained from it. 



In the foregoing observations I have assumed as correct, the state- 

 ment usually received, that the fat globules in milk are all actually 

 surrounded by envelopes. That some are so surrounded has been 

 clearly seen by Henle, Simons, and others of our latest microscopical 

 observers. Dumas long ago stated his belief that they are all so 

 enveloped, and he mentioned as a proof of it, that pure ether ex- 

 tracted no fat from new milk when mixed with it, which it could 

 not fail to do were the fatty globules naked, and simply in a state 

 of suspension. This latter statement having been called in ques- 

 tion by Voelcker, I caused new milk to be forced directly from 

 the teat of a cow, into a bottle half filled with ether, and after a 

 gentle agitation set the whole aside. Three layers formed. The 

 upper one was clear and colorless, and by spontaneous evapora- 

 tion left a considerable residue of solid ci ystalline fat, evidently 

 mixed with a fluid oil. The middle layer was semi-transparent, 

 and gelatinous, and consisted of ether, fat and curd. The third 

 or undermost layer was milk-white, and besides water and a por- 

 tion of curd, contained the sugar and salts of the milk. It is a 

 matter of after inquiry, whether by this method it can be proved 

 that the curd of milk exists in it in two separate states. 



Ether, therefore, according to this experiment, does directly 

 extract fatty matter from milk. It does not follow, however, from 

 this, that in the milk the fat globules are not really surrounded 

 by envelopes. The ether may act upon these envelopes, may 

 corrugate, shrivel, and cause them to burst, and may thus set free 

 and dissolve the fatty matter they contain. 



Natural emulsions, such as the substance of the nerves and brain 

 are considered by Mulder to contain a species of chemical com- 

 pound of the fatty matter with albumen, which has the property 

 of mixing with water. In the nerves of a dead animal, this com- 

 pound begins immediately to decompose, the fat retreating in- 

 wards and forming a transparent axis, the albumen gathering it- 

 self towards the exterior of the fibre. 



Is milk, then, a natural emulsion, which, while in the udder of 

 the cow, is under the secret influence of the vital power, and 

 which, when drawn from it, begins immediately to decompose, 



