341 
primarily, of distinguishing between fresh or raw and heated 
(pasteurized) or boiled milk. Among these may be mentioned 
guaiacum (32), potassium iodide, and starch (33), paraphenyiene- 
diamine (34), ortol (35), paradiethyl-paraphenylene-diamine (36) ursol 
(37), guaiacol (38), amidol (Leffmann (34) etc., etc. These reagents 
are used in connection with small quantities of hydrogen peroxide or 
some peroxide compound such as the persulphates, perborates, or 
ozonized oil of turpentine, and with fresh unheated milk they all 
give characteristic changes of color which are not shown by milks 
which have been heated to 80° C. or higher. 
Whether the peroxidases of milk give rise to any changes in the 
composition of the milk can at present only be conjectured. It may 
be of course that they gradually effect the oxidation of reducing 
substances in the milk. According to some authors they gradually 
disappear when the milk turns sour. It has been our experience, 
however, that they pass practically unchanged into the whey 
when milk curdles as the result of the lactic acid fermentation. 
In the present state of our knowledge the various tests which have 
been proposed for the peroxidases of milk are chiefly useful in enabling 
us to form an idea of the condition of the milk, whether it has been 
heated beyond certain temperatures or not, although according to 
Gillet (16) even normal fresh milks vary in the amounts of perox- 
idases which they contain, and this has also been our own experience 
with this reaction. 
Reductases . — According to Seligmann (39) raw milk possesses 
reducing properties; for example, it reduces Schardinger’s (40) 
reagent, which consists of a solution of methylene blue containing 
small amounts of formaldehyde. By some authors these reducing 
substances have been regarded as ferments, reductases, by others as 
due to bacteria, and by still others they have been looked upon as 
identical with catalase, the ferment in milk which decomposes 
hydrogen peroxide. By the use of a weak alcoholic solution of 
methylene blue, Smidt (41) claims to have been able to distinguish 
between the redaction brought about by bacteria and that caused 
by ferments. This author has shown that the reductases of milk are 
different from the catalase and superoxidase of milk and separable 
from these, the latter being soluble in water and salt solution, the 
former not. In recent communications Seligmann (42) points out 
that the reductases and peroxidases of cow’s milk are not identical. 
According to this author all processes of reduction occurring in fresh 
and sour milk are due to the action of bacteria and not to unorganized 
ferments. 
Cathcart (43) has also made a study of the reduction of Schar- 
dinger’s reagent by fresh milk. According to this author the reduc- 
tion of the coloring matter is due to the presence of a catalase which 
