468 THE AMERICAN NATURALIST. [VoL. XXXV. 
The essential product of respiration, the one which distin- 
guishes respiration from all the other functions of the living 
organism, is kinetic energy. The material products vary in 
kind and in quantity according to the nature of the organism 
and the substances which can be affected, these substances 
being in most cases complex compounds elaborated within the 
body of the respiring plant, but not in all cases, as shown by 
the bacteria just mentioned. 
Nor is free oxygen necessary to all organisms or to all cells. 
As the haemoglobin of the blood is a complex compound from 
which some of the oxygen, only loosely held, can be readily 
withdrawn where oxidation for the supply of energy is needed, 
so the color products of certain bacteria (e.g., Bacillus bruneus) 
are reserves of oxygen which become used when there is no 
longer an adequate supply of free oxygen.! From colorless 
compounds also, the cells at depths in the tissues of animals 
(perhaps also of plants?), to which free oxygen penetrates only 
in insufficient amounts if at all, obtain by decomposition the 
energy needed. These decompositions are not necessarily 
effected to secure oxygen for the oxidation of other sub- 
stances, for the decompositions themselves release as kinetic 
the potential energy which was holding the complex substances 
together. 
The mutual attraction of one atom of carbon and two of 
oxygen is so great as to make the molecule of carbon-dioxide 
very stable as well as very simple, for the affinities of the 
carbon and oxygen are satisfied. In the complex compounds 
of carbon, hydrogen, and oxygen in the sugar group, the affini- 
ties of the component elements are not satisfied ; the com- 
pounds are much less stable, as their ability to take up more 
oxygen shows. At ordinary temperatures and under ordi- 
nary conditions these compounds are stable. Their stability 1s 
due to the mutual affinities of their component atoms which 
exert an attraction upon one another sufficiently powerful to 
! Ewart, A. J. On the Evolution of Oxygen from Colored Bacteria, Journ. 
Linnean Soc., vol. xxxiii (1807), p. 123. 
: Pfeffer, W. Berichte d. math. phys. Klasse d. K. Sáchs. Gesells. d. Wiss. ™ 
Leipzig, 27 Juli, 1896, p. 383. 
