331 
Using an acetone solution of guaiacum (purified according to 
Portier (43) and dilute hydrogen peroxide, we made the following 
observations on the resistance of the milk peroxidases to heat : 
Temperature ; Time of exposure. 
Color with reagent. 
70 . 
5 minutes. 
Dark blue. 
Do. 
Do. 
Dark blue; slow in developing. 
None. 
Dark blue. 
Do. 
Dark blue; somewhat slow in developing. 
70 
8 minutes 
72 
10 minutes 
70 
15 minutes 
70 
60 minutes. 
60 
15 minutes. 
60 
30 minutes 
60 
60 minutes 
It is evident, therefore, that while short exposures of milk to a tem- 
perature of 60° C. are apparently without effect on the activity of the 
peroxidases, an hour’s exposure to this temperature renders them 
somewhat less active than in unheated milk, and an exposure of one 
hour to a temperature of 70° C. destroys them. 
It was also observed that milk just brought to 75° C. and 80° C. no 
longer gives the blue color with the guaiacum reagent. An examina- 
tion of curdled milk with this reagent revealed the presence of the 
peroxidase chiefly in the whey and apparently in unaltered condition 
so far as activity is concerned. 
Catalase . — Less is known concerning milk catalase than is known 
of the peroxidases. It would seem, however, that they are perhaps 
more sensitive to heat than the peroxidases. Van Itallie (44) 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. Accord- 
ing to Jolles (45) heating to 75° C. destroys the catalases of woman’s 
milk completely. Wender (20) observed that catalase prepared from 
separator slime (see galactase) becomes inactive at 80° C. 
According to Hippius (22) the bactericidal property of milk is 
retained even after long heating at 60°-65° C., but is weakened by 
a short exposure to 85° C., wheyeas according to Behring (46) 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. It is evident, therefore, from these considerations, 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 fer- 
ments can withstand somewhat higher temperatures in neutral or 
