acids than the latter ferment. The heat boundary of its activity is 
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. 
Yon Freudenreich (21) 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. Accord- 
ing to Hippius (22) 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 temperature 
of 60° for one hour, but is destroyed by heating above 75° C. 
Milk lipase . — Gillet (23) has found that milk Jipase is destroyed 
at 65° C. According to Hippius (22) 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 (22), destroyed above 65° C. However, the existence of 
this ferment is doubtful. (See p. 338.) 
Hougardv (24) has found that the activity of lactokinase is greatly 
enfeebled by heating for twenty minutes at 75° C. and practically 
destroyed by heating at 75° C. for half an hour. 
THE OXIDIZING FERMENTS OF MILK. 
While our knowledge of the soluble ferments is of too recent date 
for an exact understanding of their significance and powers of resist- 
ance, the well-known reactions of the oxidases have furnished us with 
a useful criterion for distinguishing between living (raw) and heated 
milk (Zelinski 25). 
According to Marfan (see Zelinski (25)) the oxidases of milk are 
destroyed at 79° C. According to Hippius (22) 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 (20) the peroxidase of milk 
becomes inactive at 83° C. According to Schardinger (26), using- 
methylene blue as a reagent, the critical temperature of the milk 
