339 
at present, that the fresh milk of all animals has the power of decom- 
posing hydrogen peroxide more or less easily. Jolles (21) has pointed 
out that human milk decomposes five or six times as much hydrogen 
peroxide in the same length of time and under the same conditions 
as cow’s milk. This author is inclined to attach considerable impor- 
tance to this reaction, and recently Von der Velden (22) also lays em- 
phasis on the fact that the presence of catalase in human milk serves 
to distinguish it from cow’s milk. On the other hand, the fact that 
cow’s milk can decompose hydrogen peroxide is attested by many 
observers, some of whom, among them Amberg (23), have called atten- 
tion to the gradual disappearance of hydrogen peroxide in cow’s 
milk on standing, and others, van Itallie (24) among them, to the fact 
that cow's milk loses its power to decompose hydrogen peroxide on 
heating to 63° C. Faitelowitz (25) has shown that the catalase of 
milk is associated with the fat globules. This has been confirmed by 
Reiss (26), who further points out that the catalase of milk is insolu- 
ble in the presence of colloids. 
In the present state of our knowledge we know very little concerning 
the function of catalase in living tissue and active secretions. The 
view has been advanced by Loew (27), who has made extensive 
studies in this field, that the function of catalase is to destroy any 
hydrogen peroxide that may have been formed during the respiratory 
processes in the living cell, thereby preventing the accumulation of 
this and other peroxides, all of which are more or less toxic in their 
effects, thus affording protection against a toxic product of respira- 
tion. The question whether hydrogen peroxide is formed in the res- 
piratory process in plants or animals is a much-mooted question, and 
there has been considerable difference of opinion among chemists as 
to whether hydrogen peroxide ever occurs in animal or vegetable tis- 
sues. One thing is certain, however, and that is, whether hydrogen 
peroxide occurs therein or not other complex peroxides do occur, espe- 
cially in plant tissues and exudations (see Bach’s (27a) investigations), 
and quite recently in an investigation of remarkable interest and far- 
reaching importance, Usher and Priestly (28) have confirmed Erlen- 
meyer’s (29) theory of the origin of carbohydrates in green plants, 
which supposes these substances to originate from formic aldehyde, 
which in turn results from the reaction of carbon dioxide with water, 
as indicated in the following equations : 
(1) CO, + 2H,0 = foI '" 11 y^ C1(1 + HA 
and 
(2) H 2 C0 2 + H 2 0 = 
h 2 co 2 
formic aldehvde 
H 9 C0 
+ fro,. 
