337 
Using an acetone solution of guaiacum (purified according to 
Portier (46) and dilute hydrogen peroxide) we made the following 
observations on the resistance of the milk peroxidases to heat : 
Temperature 
(°C.). 
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 
0 ' 
15 minutes 
0 
60 minutes 

60 
15 minutes 
60 
30 minutes 
60 
60 minutes 
i 
It is evident, therefore, that while short exposures of milk to a 
temperature 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. 
[Since the foregoing was written the whole subject of the peroxi- 
dase reaction of milk has been thoroughly investigated by Kastle 
and Porch (47). These observers succeeded in showing, first, that 
the power of milk to induce the oxidation of phenolphthalin and 
other leuco-compounds by hydrogen peroxide is greatly intensified 
by certain substances of the phenol type ; and that by the use of these 
peroxidase-accelerators, phenolphthalin, guaiacum, and parapheny- 
lene-diamine can all be used to advantage and with certainty as per- 
oxidase reagents for milk; second, that the fresh milks of different 
cows of the same herd exhibit considerable differences in peroxidase 
activity; third, that by means of the peroxidase reaction thus modi- 
fied it is possible to distinguish between raw and cooked milk or 
between raw milk and that which has been sterilized at a temperature 
of 70° C. or higher for short intervals, and that while milks which 
have been heated to 70° C. for one hour, or to 75° C. for twenty 
minutes, no longer show the peroxidase reaction, this reaction is not 
diminished in intensity, but, if anything, somewhat increased, by 
heating the milk to 60° C. for twenty minutes. It is evident, there- 
fore, that the pasteurization of milk at 60° C. for twenty minutes, 
as recommended by Posenau, does not destroy the biological proper- 
ties of milk, at least so far as we are able to judge from the per- 
oxidase reaction.] 
1414— Bull. 56—09 22 
