434 LIQUID PARTS OF ANIMALS. 



It is impossible to state the proportion of casein which exists 

 in milk, because it varies so much, not only in the milk of dif- 

 ferent animals, but also in that of the same animal at different 

 times. According to Berzelius 100 parts of skimmed-milk which 

 he analyzed contained 2-8 of casein. 



Lassaigne made a curious remark respecting the milk of a cow, 

 which he examined at ten different periods ; four of these before par- 

 turition and six after it. The milk examined during the first three 

 of these periods, namely, forty- two days, thirty- two days, and twen- 

 ty-one days before parturition, contained no casein at all, but in 

 place of it albumen. The milks examined eleven days before and 

 just after parturition contained both albumen and casein ; the milks 

 examined four days, six days, twenty days, twenty-one days, and 

 thirty days after parturition, contained casein and no albumen.* 

 It would have been of importance had Lassaigne informed us of 

 the method which he followed to distinguish casein from albu- 

 men, and to separate them from each other when they existed to- 

 gether in milk. 



3. Whey, after being filtered to separate a quantity of curd, 

 which usually floats through it, is a thin pellucid fluid of a yel- 

 lowish green colour and an agreeable and sweetish taste, in which 

 the flavour of milk may be distinguished. Almost the whole 

 curd may be separated by keeping the whey for some time at a 

 boiling temperature. A thick white scum gathers on the surface, 

 known in Scotland by the name ofjftoat whey. When this scum, 

 which consists of the curdy part, is carefully separated, the whey, 

 after being left at rest for some hours to give the remainder of 

 the curd time to separate, is quite transparent, and much less 

 coloured than before. It still retains its sweet taste, but much 

 of the milky flavour is dissipated. If it be now evaporated over 

 the steam bath it deposits a number of crystals of sugar of milk. 

 Towards the end of the evaporation some crystals of chloride of 

 potassium and some of common salt, make their appearance.f 

 According to Scheele it contains also a little phosphate of lime, 

 which may be precipitated by ammonia. :f 



Schwarz found that 1000 parts of cow's milk left 3-697 of 

 ashes, composed of 



* Ann. de Chim. et de Phys. xlix. 35. 

 " f Parmentier, Jour, de Phys. xxxvii. 417. 

 | Scheele's Essays, ii. 61. 



