36 MILK [in 



presence of these substances, however, is of little 

 importance. 



Gases in Milk. Lastly, we have oxygen, nitrogen, 

 and carbonic anhydride in varying amounts. Of 

 dissolved nitrogen the amount may be stated at '75 

 per cent ; dissolved oxygen 1 per cent ; free carbonic 

 anhydride *7 '5 per cent, and in a combined form from 

 01 to *2 per cent (Kirchner). 



The constituents of milk are thus partly in a state 

 of emulsion (the fat), partly in a state of suspension 

 (caseous matter, lime, magnesia, phosphoric acid), and 

 partly in a state of solution (albumin, milk-sugar, 

 and most of the mineral matter). 



The Reaction of Milk. The reaction exhibited 

 towards different vegetable colouring substances by 

 milk varies. Human milk is normally alkaline in 

 its reaction, while that of carnivorous animals is 

 generally acid. With regard to cows' milk, how- 

 ever, the very curious fact has been observed that it 

 exhibits the so-called amphoteric reaction; that is, 

 both an acid and alkaline reaction. This is due to 

 the presence in it of acid and neutral phosphates and 

 carbonates of the alkalies. 



Sheep's, Goats', and Mares' Milk. With regard 

 to sheep's, goats', and mares' milk, it may be men- 

 tioned that the first named possesses a yellowish- 

 white colour and is characterised by a high per- 

 centage of total solids, which consist chiefly of fat 



