286 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



agitated must not be mistaken for curds or flakes result- 

 ing from the alcohol reaction. 



The 68 per cent, alcohol is made by mixing 68 parts of 

 absolute alcohol with 32 parts of distilled water. The 

 alcohol should be neutral. This can be determined by 

 adding a few drops of phenolphthalein solution to a small 

 quantity of the alcohol and then running in a drop of 

 tenth-normal sodium hydroxide solution. If the alcohol 

 is neutral the mixture will assume a permanent pink 

 color. 



Fresh normal market milk will not curdle when 

 tested in this manner. Milk which has undergone acid 

 fermentation, or which has been acted upon by the rennet- 

 like ferment produced by certain species of bacteria, or 

 which has undergone a combined acid and rennet fermen- 

 tation, will curdle when these processes have operated to 

 a certain extent. A positive reaction therefore results 

 when the milk has undergone a certain degree of bacterial 

 decomposition and is an indication that the milk is old, or 

 that it was produced under unclean conditions, or that it 

 was not properly cooled and cared for. 



The milk of individual cows will give a positive reac- 

 tion for from four to twelve days after parturition and 

 near the end of lactation. For a rather long time after 

 abortion, the milk will also give a positive reaction. Milk 

 from cows with diseased udders will react positively be- 

 fore any clinical symptoms are apparent and also for a 

 time after the disease has clinically healed. Milk from 

 cows affected with diseases or injuries of the genital tract, 

 diseases of the digestive tract, or advanced tuberculosis 

 will also usually give a positive reaction to the alcohol 

 test, but not always. It appears that a positive reaction 

 occurs in these cases only when pathological products are 



