104 MILK 



3. During aeration the carbon dioxid of the pumped gases 

 dropped still farther by aeration over glass, tin, copper, and 

 through glass wool. The oxygen increased at the same time._ 



4. Below a certain percentage the elimination of carbon dioxid 

 becomes very difficult. 



5. Air confined over sterilized milk indicates no interchange of 



gases. • -1 



6. Most micro-organisms in milk generate carbon dioxid and 



absorb oxygen. 



7. Milk fresh from the cow and confined in a flask consumes the 

 oxygen and liberates carbon dioxid. 



8. Free carbon dioxid in amounts of 100, 96.5, and 62.9 per 

 cent, have a marked restraining action on bacteria, and in some 

 cases an inhibitive action. 



9. Free carbon dioxid has a direct influence upon the character 

 and rate of milk fermentations induced by specific micro-organ- 

 isms. 



10. Confined milk does not ferment more readily than aerated 

 milk. Aeration does not influence the amount of oxygen supply 

 to the bacteria present. 



11. Milk exposed freely to the air decreases in acidity for a 

 few hours after milking, then the acidity rises rapidly. Con- 

 fined milk does not show a decrease in acidity after milking. 



12. Carbon dioxid is one factor which keeps up the acidity 

 of confined milk with phenolphthalein as indicator. 



13. Closing milk-cans from the air reduces the amount of 

 oxygen supply, therefore must change the conditions of germ 

 fife. 



14. Aeration does not change the germicidal action of milk. 



15. Aeration does influence the amount of oxygen supply to 

 the bacteria present. 



The Reaction of Milk 



Fresh milk from most mammals reacts acid to rosolic acid and 

 phenolphthalein, amphoteric to litmus, and alkaline to dimethyl- 

 orange. Milk from carnivorous animals is usually more acid than 

 milk from herbivorous animals. The acidity is due to acid 

 phosphates, citrates, and casein; the alkalinity, to alkahne phos- 

 phates. Red litmus is turned blue; blue litmus, red. Carbon 

 dioxid is partly responsible for the acid reaction and, since the 

 carbon dioxid content decreases when milk is in contact with the 

 air, there is a decrease in acidity for three to four hours after 

 milking. After a lapse of about four hours the acidity increases 

 rapidly, due to the activity of micro-organisms. 



Raudnitz found that 1 liter of cow's milk required 17.5 c.c. of 



