648 
The heating of the milk produces a decomposition of the albumi- 
noid matter, manifesting itself by the production of a little hydrogen 
sulphid. This gas may also be produced by the action of micro- 
organisms. 
It is claimed that the heating of milk renders a part of the phos- 
phates insoluble, and that this change favors rachitis in children arti- 
ficially fed with it. On the other hand it appears to be the general 
opinion of physicians that rachitis is the result of defective alimenta- 
tion, due to causes other than the changes in heated milk. 
The heating of milk for half an hour at a temperature of 150° F. 
(65° C.) or over, has the effect of entirely preventing the rising of 
the cream or of delaying it very materially. In normal milk the 
larger proportion of the fat droplets agglutinate into tiny globules 
or masses. At a temperature of 65° C. or above, these clusters are 
broken down and the globules are more homogeneously distributed 
throughout the fluid. 
The cooked or scalded taste appears at about 70° C., and becomes 
more pronounced the higher the temperature. This is due perhaps to 
changes in the nitrogenous products in the milk. The loss of certain 
gases also alters the taste, so that milk heated in closed vessels has a 
much less pronounced flavor than if heated in open vessels. 
Milk sometimes curdles in the process of pasteurization. This is 
due to the amount of acid and calcium salts which it contains. In 
order to avoid such accidents, Kastle advises that the only safe rule 
to follow is to determine the effect of heating on small samples of the 
milk, which it is proposed to pasteurize. 
It has been observed that cooked milk coagulates with rennin more 
slowly than raw milk. This effect is noted often at temperatures of 
80° to 90° C., but it has not been observed in milk heated to 60° for 
twenty minutes. The curd produced by rennin coagulation in cooked 
milk is softer, less tough, and more flocculent than that produced by 
rennin coagulation in raw milk. This is believed to be an advantage 
favoring the digestibility of heated milk. 
TEMPERATURE AND TIME OF HEATING. 
The two dominant factors that control the temperature and time 
at which the milk should be pasteurized are, (1) the thermal death 
points of pathogenic bacteria, and (2) the ferments in the milk. The 
first must be surely killed so as to eliminate this danger, and the sec- 
ond should not be affected sufficiently to “ devitalize ” the milk.® 
a Reference to ttie article upon “ The germicidal property of milk,” Rosenau 
and McCoy, p. 455, shows that a temperature of 60° for twenty minutes but 
slightly affects this property of freshr raw milk. In old milk the so-called 
germicidal action ” disappears spontaneously. 
