335 
influenced by the chemical reaction of the solution in which it is 
present, being lower in acid than in neutral or alkaline solution. 
When galactase that has been heated to 70° C. for ten minutes is 
added to milk, the digestion is slowed, and heating to 76° C. for ten 
minutes entirely destroys its digestive powers. In the Fermi (19) 
gelatin tests no digestion took place with specimens of the ferment 
that had been heated to 65° C., whereas with the unheated controls, 
the gelatin liquefied. 
Von Freudenreich (22) has confirmed the observations of Babcock 
and Russell on galactase. According to this observer a temperature 
of 75° C. for half an hour causes a falling off in the proteolytic 
activity of this enzyme. On the other hand, he found an exposure 
to 60° C. for half an hour to scarcely weaken it to a noticeable degree. 
According to Hippius (23) the proteolytic ferments of milk can 
withstand an exposure to 60° C. for one hour and an exposure to 
65° C. for half an hour. 
Milk amylase, according to this author, can withstand a tempera- 
ture of 60° for one hour, but is destroyed by heating above 75° C. 
Milk lipase . — Gillet (24) has found that milk lipase is destroyed 
at 65° C. According to Hippius (23) the lipase of woman’s milk can 
withstand a temperature of 60° for one hour and a short exposure to 
62°, but is weakened at 63° C., and is destroyed at 64° C. 
The salol-splitting ferment (Nobecourt and Merklen) is, according 
to Hippius (23), destroyed above 65° C. However, the existence of 
this ferment is doubtful. (See p. 344.) 
Hougardy (25) has found that the activity of lactokinase is greatly 
enfeebled by heating for twenty minutes at 75° C. and practically 
destroyed by heating for half an hour at this temperature. 
The oxidizing ferments of milk . — While our knowledge of the solu- 
ble ferments is of too recent date for an exact understanding of their 
significance and powers of resistance, the well-known reactions of 
the oxidases have furnished us with a useful criterion for distin- 
guishing between raw (living) and heated milk (Zelinski 26). 
According to Marfan (see Zelinski (26)) the oxidases of milk are 
destroyed at 79° C. According to Hippius (23) they can withstand 
a temperature of 60° C. to 65° C., but are destroyed by a short 
exposure to 76° C. 
Peroxidases . — According to Wender (21) the peroxidase of milk 
becomes inactive at 83° C. According to Schardinger (27), using 
methylene blue as a reagent, the critical temperature of the milk 
peroxidases is 80° C. With Arnold’s guaiacum reagent milks heated 
to 80°, according to Ostertag, failed to show the reaction (see Glage 
(28)). Franz Utz (29), using Schaffer’s (30) reagent, found that 
milk heated for a short time at 90° C. or a long time at 70° C. failed 
