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 
