582 USE or milk in the animal economy. 



only 2 lbs., at others as much as 7 lbs. of ash.- This ash consists of a 

 mixture of common salt and chloride of potassium (p. 188), with the 

 phosphates of lime, magnesia, and iron. The relative proportions of 

 these several substances yielded by 1000 lbs. of the railk of two dif- 

 ferent cows, were as follows [Haidlen, Annal. der Chem. und Phar., 

 xiv., p. 273] : 



I. II. 



Phosphate of lime 2-31 lbs. 3-44 lbs. 



Phosphate oi" magnesia . . . 0-42 " 0-64 " 



Phosphate of peroxide of iron . 0-07 " 0'07 ♦' 



Chloride of potassium .... 1-44 " 1-83 " 



Chloride of sodium 0-24 " 0-34 '* 



Free soda 0-42 " 0-45 " 



4-90 " 6-77 " 



It is probable that the phosphates and chlorides existed as such in the 

 milk as it came from the cow, the free soda is believed to have been in 

 combination with the casein, and to have held it iti solution in the milk. 

 You will recollect that the explanation I have given of the curdling of 

 milk is, that the acid produced in, or added to, the milk, takes this soda 

 from the casein, and renders it insoluble in water, and that in conse- 

 quence it separates in the form of curd (see p. 566). 



§ 25. Purposes served by milk in the animal economy. 



Milk is the food provided for the young animal, at a period when it is 

 unable to seek food for itself. It consists, as we have seen, of — 



1°. The casein or curd. — This being almost identical in constitution 

 with the lean part or fibrin of the muscles serves to promote the growth 

 of the flesh of the animal. 



2°. The fat or butter^ which is mainly expended in supplying fat to 

 those parts of the body in which fat is usually deposited. 



3°. The sugar, which is probably consumed by the lungs during re- 

 spiration. 



4°. The saline matter, from which come the salts contained in the 

 blood, and the earthy part of the bones of young and growing animals 

 fed upon milk. 



These several purposes served iH milk will come again under our 

 consideration in the following lecture. 



NOTES. 

 1°. On the churning of butter in the French chum. 

 Mr. Burnett, of Gadgirth, has favoured me with the following infor- 

 mation regarding the merits of the French churn mentioned in page 

 555:— 



" I see you make mention, in page 555 of your Lectures, of a chum 

 lately introduced by Mr. Blacker from France. I got one of these from 

 Mr. Blacker about two years ago, and have proved its merits to be very 

 great. I use none else, and have been the means of distributing it over 



