MILK. 429 



name of beist. The same term, I believe, is applied to it in En- 

 gland. 



When milk is allowed to remain for some time at rest there 

 collects on its surface a thick unctuous, yellowish-coloured sub- 

 stance, known by the name of cream. 



After the cream has separated, the milk which remains is much 

 thinner than before, and has a bluish white colour. If it be 

 heated to 100 and a little rennet (water digested with the inner 

 coat of a calf's stomach and preserved with salt,) be poured into 

 it, coagulation ensues. If the coagulum be broken the milk soon 

 separates into two distinct substances ; a solid white part known 

 by the name of curd, and a fluid portion called whey. Thus 

 milk is easily separated into three distinct substances, namely, 

 cream, curd, and whey. 



1. Cream is a semiliquid of a yellow colour, and its consistence 

 increases gradually by exposure to the atmosphere. In three 

 or four days it becomes so thick that the vessel containing it may 

 be inverted without risking any loss. In eight or ten days more 

 its surface is covered over with mucors and byssi, and it has no 

 longer the flavour of cream but of very fat cheese.* In this 

 state it constitutes what in this country is called cream cheese. 



The quantity of cream yielded by milk varies not only in dif- 

 ferent animals, but in the same animal at different times. The 

 following table shows the ratio between the bulks of cream and 

 whey from the same cow, (fed on beet-root, hay, and straw,) at 

 different periods before and after parturition, as determined by 

 Lassaigne :f 



Volume of Volume of Water 



cream. whey. per cent. 



42 days before parturition, 200 . 800 . 78-4 



32 ditto, . 200 . 800 . 78-2 



21 ditto, . 200 . 800 . 78-1 



11 ditto, . 200 . 800 . 78-8 



Just after parturition, 200 . 800 . 78-2 



4' days after ditto, 200 . 800 . 79.8 



6 ditto, . 188 . 812 . 82-0 



20 ditto, . 78 . 922 . 89-0 



21 ditto, . 59 . 941 . 88-0 

 30 ditto, . 64 . 936 . 90-0 



* Jour, de Phys. xxxvii. 372. f Ann. de Chim. et de Phys. xlix. 35. 



