MILK. 203 



fed to cows. And this acid may very easily be taken 

 into the system of the cow and directly atfect the con- 

 dition of the milk, causing it to be distinctly acid in- 

 stead of alkaline, as it should be naturally. Moreover, 

 as this acid may be very easily, and is no doubt often, 

 produced in the course of the digestion of the food in the 

 cow's stomach, it is readily seen how most unexpected 

 difficulties may arise in the dairy in the summer to vex 

 and discomfit the dairyman. 



Acid is the most treacherous and effective agent of 

 change in milk, cream, and butter. It should be 

 watched for at every turn and neutralized by every pos- 

 sible means. The addition to the milk of a small quan- 

 tity of soda will take up the acid as fast as it is formed, 

 and will remain as lactate of soda in the milk in an inert 

 and harmless condition ; but to avoid the presence of 

 this acid the food and every utensil used in the stable, 

 feeding jDrocess, and in the care of the milk should be 

 kept most rigidly free from acidity. 



But another fact still remains to illustrate the excess- 

 ive instability of milk. Caseine, of which about four per 

 cent is dissolved in the milk, is itself able to change milk 

 sugar into this milk (lactic) acid. Many nitrogenous 

 substances possess this peculiar power. Gluten of wheat, 

 animal membranes, as a piece of bladder or of the gut or 

 stomach of an animal, as well as the legumin of peas 

 and beans and the caseine of milk, exert this effect. 

 Some time or enabling effect, however, is required to de- 

 velop this property in caseine, and exposure to air and 

 warmth for a certain period are sufficient to develop it. 



And upon this fact another most important one bears, 

 viz., that caseine in this active condition has the effect 

 of changing milk sugar first into lactic acid, and then the 

 lactic acid into butyric acid, which is the active agent of 

 rancidity in butter, and is the cause of the greatest" diffi- 

 culties wJiich the dairyman meets with in the warm 



