338 
Catalase. — Less is known concerning milk catalase than is known 
of the peroxidases. It would seem, however, that it is perhaps more 
sensitive to heat than the peroxidases. Van Itallie (48) has shown 
that cow's milk is unable to decompose hydrogen peroxide after an 
exposure of one-half hour to 63° C. On the other hand, human milk 
still retains this power after a similar exposure. According to Jolles 
(49), heating to 75° C. destroys the catalases of woman's milk com- 
pletely. Vender (21) observed that catalase prepared from separa- 
tor slime (see galactase) becomes inactive at 80° C. 
Other biological properties. — According to Hippius (23) the bac- 
tericidal power of milk is retained even after long heating at 60°-65° 
C., but is weakened by a short exposure to 85° C., whereas according 
to Behring (50) this property of milk is lost after an hour’s heating 
to 60° C. 
The alexins of milk, according to Behring, are affected by heat in 
exactly the same way and to the same extent as the antibacterial sub- 
stances. Lane-Claypon (51) has shown that on adding blood 
corpuscles to milk the cream picks them up and carries them to the 
top, and that this property of milk is destroyed by heating it to 70° 
C. for a few minutes. It is evident, therefore, from these considera- 
tions, that the thermal death point of the milk ferments is dependent 
on a number of conditions besides the temperature itself. Chief 
among these are time and the reaction of the medium. As a rule, 
the soluble ferments can withstand somewhat higher temperatures in 
neutral or slightly alkaline solution than in acid solution. Acidity 
and temperature naturally augment the destructive powers of each 
other toward the enzymes. This accounts for the apparent dis- 
crepancies existing among such observations. In general, it may be 
said, however, that the milk ferments, most of them at least, can 
withstand a temperature ranging from 60°-65° C. for some time, 
without material injury. Between 65° C. and 70° C. most of them 
are weakened in their activities, and between 70° C. and 80° C. all 
of them are destroyed, even after relatively short exposures. 
According to Kaudnitz (52) all the ferments of milk are destroyed 
between 75° C. and 90° C. (See also Tjaden. Koske, and Hertel (53), 
and also E. TVeber (54), for further information bearing on this 
point.) 
The digestibility of raw and heated milk. — In this connection the 
effect, of heat on the digestibility of milk proteids has been the sub- 
ject of considerable investigation. According to Kerr (55) milk is to 
be looked upon as consisting of living cells suspended in serum, the 
former consisting of fat cells and nucleated cells of the nature of 
white blood corpuscles. (As a matter of fact it has been definitely 
proven that leucocytes do actually occur in milk — see p. 491.) Ac- 
cording to Kerr, when milk is ingested, these living elements are at 
