No. 414.] NORMAL RESPIRATION. 475 
either as component parts of these tissues or as parasites or 
saprophytes therein ; in the deeper layers of compact soils, in 
the mud of swamps and marshes, and in the ooze below bodies 
of comparatively still water, fresh and salt. 
As in aérobic, so also in anaérobic respiration, other proc- 
esses take place simultaneously with it. These, if not directly 
caused by respiration, are at all events maintained by the 
energy liberated in respiration and are so closely connected 
with it that to distinguish between the chemical products of 
respiration and those of the processes accompanying it, is a 
matter extremely difficult and still only imperfectly accom- 
plished. Fermentation, decay, and disease at least accompany, 
if they are not actually a part of, the respiratory processes of 
certain low plants. Respiration, anaérobic as well as aérobic, 
is a function of the living protoplasm, which acts upon sub- 
stances enclosed within its own body, producing simpler 
substances of which some remain in the respiring cell while 
others diffuse out of it. Some of the latter are chemically 
inactive, like carbon-dioxide and alcohol; others may act on 
substances outside the cell. In higher animals and plants the 
enzymes (e.g., pepsin, diastase, etc.) are produced in connec- 
tion with the process of nutrition, converting the substances 
upon which they act into available food compounds; but it is 
also certain that, among the enzymes produced, there are some 
which bring about such changes in the surrounding substances 
that these become available as sources of kinetic energy. 
The diastase formed in the germinating seed, dissolving the 
Starch deposited in the seed as a reserve food and converting it 
into sugar, makes the reserve food available for at least three 
purposes: first, for the construction of nitrogenous compounds 
(amides and proteids); second, for the formation of cell-wall 
(cellulose); 74777, for the liberation of energy by respiration. 
The production and action of this enzyme furnishes material 
for respiration, nutrition, and growth. The enzymes formed 
by lower plants are also useful in more than one way, not the 
least important use being the conversion of irrespirable into 
respirable substances. 
LELAND STANFORD JR. UNIVERSITY. 
