647 
When the milk reaches about 60° C., a scum forms on the surface 
which consists of — 
Per cent. 
Fatty matter 45. 42 
Casein and albuminoid 50. 80 
Ash 3. 72 
Milk heated in closed vessels does not form a pellicle even when 
the temperature reaches 100° or 110° C. Milk heated in the open 
air. after cooling forms a pellicle on the surface which renews itself 
if it is removed. It seems that this pellicle is due mainly to the 
drying of the upper layer of the liquid. The cream probably does 
not rise well in heated milk, owing to the increase in the viscosity of 
the liquid in which it is emulsified. 
Heat kills the ferments in milk,® which according to some authors 
play a useful role in digestion and metabolism. We have no direct 
knowledge of the utility of these milk ferments. For the child to 
digest and assimilate cow’s milk to advantage the complex albumi- 
nous ‘substances must first be broken down by the processes of digestion 
into simpler products and again synthetized. In other words, cow 
proteins must be converted into human proteins. In this process fer- 
ments play an essential role. We know that the digestive tube con- 
tains ferments that dissolve and break up the complex proteins into 
simpler substances, but concerning the rearrangement of the molec- 
ular structure into the form best suited for assimilation we have 
little definite knowledge. While ferments play an active part in 
both the breaking down and the building up processes, it remains for 
future investigation to determine which particular ferments are help- 
ful in the latter process. It has been abundantly shown by laboratory 
work that the ferments in milk, or most of them, at least, can with- 
stand a temperature ranging from 60° to 65° C. for some time with- 
out material injury. Between 65° and 70° most of these are weakened 
in their activity, and between 70° to 80° all of them are destroyed, 
even after relatively short exposure. (Kastle.) 
Raw milk shows the peroxidase reaction, whereas milk which has 
been heated for one hour at 70° C., or for shorter intervals at higher 
temperatures, does not exhibit this reaction. In this connection 
Kastle and Porch have observed that on heating milk to 60° C. for 
20 minutes, the peroxidase reaction of many specimens of milk is not 
only not diminished but if anything somewhat intensified. 
® Hippius (Deut. med. Woch., vol. 27, 1901, p. 481, 502) states that the oxi- 
dizing ferments are able to withstand temperatures between 60° and 65° C. for 
a long time, but are destroyed after a short exposure to 76° C. The lipase, or 
fat-splitting ferment, withstands one hour’s heating at 60° C., or 62° for a 
short time; is weakened at 63°, and destroyed at 64° C. The proteolytic fer- 
ment withstands one hour’s heating at 60° or half an hour at 65° C. The amy- 
lase withstands one hour at 60° and is only destroyed at 75° C. (See also 
Kastle and Roberts’s article, No. 10, p. 313, this bulletin.) 
