DETECTION OF ADULTERATION 49 
mining whether a given sample has been thus heated. 
In most cases the action of the enzym is in- 
dicated by the production of a deep blue, no 
color change occurring when the enzym has been 
heated. Hydrogen peroxid is commonly em- 
ployed for furnishing the oxygen. A considerable 
number of substances have been found to be 
susceptible to oxidation under: the influence of 
the milk enzyms. Benzene derivatives, com- 
monly used as photographic developers are 
especially susceptible. Guaiacum was first used. 
Arnold’s Method—A solution of guaiacum in 
acetone is, according to Arnold and Menzel 
better than the ordinary tincture. The test is 
applied by adding to a small amount of the sample. 
in a test-tube, about 1o drops of the guaiacum 
solution, to which a drop or two of hydrogen 
peroxid solution has just been added, so that the 
reagent will float on the milk. If the sample 
has not been heated above 80°, the point of 
contact of the liquids will show a deep blue ring. 
As guaiacum is liable to changes both in the 
solid form and in solution it is important to de- 
termine if the reagent is sensitive to raw milk, 
hence a control test should aways be made. 
Other reagents are now available which are, in the 
main, more trustworthy. 
Dupouy’s Method.—In this method, 1-4 diam- 
inobenzene is used. The reagent is dissolved in 
