119 
According to Bach and Chodat ( 28 ), therefore, the oxygenases are 
of the nature of substituted peroxides. They are exceedingly unsta- 
ble and have, as compared with the peroxidases, only a limited 
distribution in the vegetable kingdom. On the other hand, the 
peroxidases are characterized by great stability. Thus the peroxidase 
of the horse-radish root is not completely destroyed by a single boiling 
of its solution. The peroxidases occur in practically every plant thus 
far examined for them, and they have likewise been found widely 
distributed in the tissues and secretions of animals, such as the leu- 
cocytes, milk, saliva, etc. Like the oxidases, the peroxidases have 
been found to contain manganese, and to this element Bach and 
Chodat ( 31 ) ascribe their activity. They are also disposed to regard 
them as true ferments, although they gradually lose their activity and 
ultimately disappear as the result of the oxidations which they bring 
about. 
It would seem, therefore, that it is not the oxidase but rather the 
peroxidase which is the most important agent in plant and animal 
oxidations, inasmuch as it would render active the oxygen occurring 
in any peroxide combination whatsoever, whether it be hydrogen 
peroxide, an organic peroxide, or an oxygenase. 
Indeed, according to Moore and Whitley ( 306 ) the peroxidases are 
the only true ferments participating in biological oxidations. Ac- 
cording to these authors, Bach's so-called oxygenase is merely an 
unstable peroxide resulting from the action of the oxygen of the air 
on some readily oxidizable substance contained in the plant or animal 
tissue. From their standpoint the only essential differences between 
a tissue showing, oxidase reactions and one showing only peroxidase 
reactions is that the former contains, in addition to the peroxidase, 
a store of naturally formed peroxides, which are very unstable toward 
heat, whereas the latter contains only the ferment (peroxidase). In 
this connection it was long ago pointed out by Bach ( 18 ), and also by 
Kastle and Loevenhart ( 244 ), that the oxidizing ferments (oxidases) 
were not true ferments for the reason that they present many close 
resemblances to the organic peroxides, and for the further reason 
that they are not true oxygen-catalysts in the sense of being unable 
to accomplish the oxidation of practically unlimited amounts of 
oxidizable material. In the writer’s opinion, therefore, the objections 
which have been recently urged against the prevailing conceptions 
regarding the oxygenases are well taken. It should be borne in mind, 
however, that the precursors of the oxygenases are unstable toward 
heat and hence possess, to some degree at least, the characteristics of 
biologically active substances. 
