330 
peroxidases is 80° C. With Arnold’s guaiacum reagent milks heated 
to 80°, according to Ostertag, failed to show the reaction (see Glage 
(27)). Franz Utz (28), using Schaffer’s (29) reagent, found that 
milk heated for a short time at 90°C. or a long time at 70° C. failed to 
show any reaction, Rullmann (30) gives the following data bear- 
ing on the stability of the peroxidases of milk, as shown by Storch’s 
p-phenylene-di amine reagent : 
1. Raw milk, not heated. 
2. Milk heated one hour, 68°-69° 
3. Milk heated one-half hour, 72° 
4. Milk heated one-half hour, 90° 
5. Milk boiled one-half hour. 
greenish blue at once. 
°l . 
C. >No coloration after ten minutes. 
V. Storch (31) employing his own reagent found that exposure of 
the milk to a temperature of 75° C. for two minutes prevented the 
reaction. Freeman (32) working with Storch’s reagent found a 
temperature of 78° C. to destroy the peroxidase of milk. Du Roi 
and Kohler (33) have employed hydrogen peroxide and the potassium- 
iodide-starch reagent and have found 80° C. to be the limit of the 
reaction. Weber (34) recommends Arnold’s (35) reagent (guaiacum 
in acetone), and finds the temperature limit of the reaction to be 
about 80° C. Franz Utz (36), using a solution of ursol D, finds that 
milks which have been heated to 80° or above fail to give the peroxi- 
dase reaction. According to Rullmann (37) practically all bacteria 
are destroyed in cow’s milk by heating it for one hour to 68°-69° C. ; 
whereas, using p-phenylene-diamine hydrochloride, which he found 
to be the most delicate reagent for the peroxidase, he found that the 
latter was not destroyed unless the temperature exceeded 70° C. 
According to Van Itallie (38) the peroxidases of milk are not destroyed 
below 80° C., and milk sold as pasteurized milk gave the test with 
paraphenylene diamine and hydrogen peroxide.® Bruere (39) 
observed that milk which had been pasteurized at 80° C., or boiled, 
failed to show the peroxidase reaction with the guaiacol reagent. 
Dupouy (40) using freshly prepared paraphenylene diamine and 
hydrogen peroxide found that unheated milks gave a blue color, 
whereas those heated above 79° C. gave no color with this reagent. 
Douglas (41) using ortol as a reagent found that heating for five 
minutes at 75° C., or one minute at 80° C., destroys the peroxidase 
of milk. Marfan and. Gillet (42), using guaiacol as a reagent for the 
peroxidases in milk, found the ferments still active at 70° C. They 
were weakened at 75° C., however, and were destroyed at 78° C. to 
79° C. 
a We have also found pasteurized milk to show the peroxidase reaction, with 
guaiacum, p-phenylene-diamine and also with phenol phthalin. 
