336 
to show any reaction. Rullmann (31) gives the following data bear- 
ing on the stability of the peroxidases of milk, as shown by Storch’s 
p-phenylene- diamine reagent : 
1. Raw milk, not heated. 1 
2. Milk heated one hour, 68°-69° C. } Deep greenlsh blue at onee ' 
3. Milk heated one-half hour, 72° C. j 
4. Milk heated one-half hour, 90° C. I Xo coloration after ten minutes. 
5. Milk boiled one-half hour. 
V. Storch (32), employing his own reagent, found that exposure of 
the milk to a temperature of 75° C. for two minutes prevented the 
reaction. Freeman (33), working with Storch ? s reagent, found a 
temperature of 78° C. to destroy the peroxidase of milk. Du Roi and 
Kohler (34) have employed hydrogen peroxide and the potassium- 
iodide-starch reagent and have found 80° C. to be the limit of the 
reaction. Weber (35) recommends Arnold's (36) reagent (guaiacum 
in acetone), and finds the temperature limit of the reaction to be 
about 80° C. Franz Utz (37), 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 (38) 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 (39) the peroxidases of milk are not de- 
stroyed below 80° C., and milk sold as pasteurized milk gave the test 
with paraphenvlene diamine and hydrogen peroxide.® Bruere (40) 
observed that milk which had been pasteurized at 80° C.. or boiled, 
failed to show the peroxidase reaction with the guaiacol reagent. 
Dupouy (41), 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 (42), 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 (43), 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. Macadie (44) found that nearly all photographic developers, 
together with small amounts of hydrogen peroxide, give characteristic 
color reactions with milk which has not been heated above 75° C. 
Wilkinson and Peters (45), using benzidine and hydrogen peroxide, 
failed to obtain the peroxidase reaction with milks which had been 
heated to 78° C. or higher. 
a We have also found pasteurized milk to show the peroxidase reaction, with 
guaiacum, p-phenylene-diamine and also with phenolphthalin. 
