472 THE AMERICAN NATURALIST. [Vor. XXXV. 
is inherent in all organisms, that in the majority of organisms 
and of their component cells this power is little needed and 
hence is practically undeveloped; but that, owing to the posi- 
tion of some cells deep in the tissues of many organisms and 
to the peculiar habits of some of the lowest organisms, these 
are obliged to obtain energy in this way and have developed 
their inherent power to a high degree. 
Intramolecular respiration is the name given to this mode of 
respiration, a term not explicitly descriptive and therefore not 
entirely satisfactory. The German term Spaltungsathmung is 
in this regard more satisfactory, but it is not concisely translat- 
able. Ordinary respiration is physiological oxidation or physi- 
ological combustion or aérobic respiration. It is dependent 
upon free oxygen and yields needed kinetic energy only by 
the union of free oxygen with combustible substances. Intra- 
molecular respiration is physiological simplification of complex 
compounds or physiological rearrangement of atoms or anaé- 
robic respiration. It takes place only when free oxygen is 
present in small quantity or is altogether absent. The results 
of the two processes are the same in kind — the liberation of 
the kinetic energy needed to continue living — but, as the 
figures quoted above show, not the same in degree. 
Intramolecular respiration was first observed somewhat more 
than a hundred years ago by Rollo,! but only within the last 
few years has the connection between intramolecular and ordi- 
nary respiration been clearly demonstrated. Pasteur and other 
bacteriologists have contributed quite as much as animal and 
plant physiologists to our present knowledge of respiration. 
Pasteur and his followers have shown the peculiar habit of a 
large number of microórganisms of being active only when 
free oxygen is absent. When free oxygen is present, they 
are inactive, though they may remain alive. There is a chain 
of allied process: first, physiological respiration, or what may 
be called intramolecular respiration, the normal respiration 
of most organisms; second, physiological rearrangement 0 
atoms into simpler molecules, intramolecular respiration, the 
mode of respiration to which many cells and even organisms 
1 Rollo. Annales de Chimie, t. 25, 1798. 
