26 PLANT PHYSIOLOGY 



cells this power is little needed and hence is practically un- 

 developed ; but that, owing to the position of some cells 

 deep in the tissues of many of the larger organisms, and to 

 the peculiar habits of some of the lowest organisms, these 

 are obliged to obtain needed energy in this way and have 

 developed their inherent powers to a high degree. 



Intramolecular respiration is the name given to this 

 mode of respiration, a term not entirely satisfactory, for it is 

 not explicitly descriptive. The German term Spaltuugsatl 

 mung is in this regard much more satisfactory, but it is not 

 concisely translatable. Ordinary respiration, physiological 

 oxidation or physiological combustion, is aerobic respira- 

 tion — respiration which is dependent upon free oxygen, and 

 which yields the needed kinetic energy only by the union of 

 free oxygen with combustible substances. Intramolecular 

 respiration, physiological simplification of complex sub- 

 stances, physiological rearrangement of atoms, is anaerobic 

 respiration — respiration which takes place only when free 

 oxygen is present in insuflScient quantities or is altogether 

 absent. The results of the two processes are the same in 

 kind — the liberation of the kinetic energy necessary to con- 

 tinue living — but not the same in degree, as the figures 

 above quoted show. 



It is now about one hundred years since intramolecular 

 respiration was first observed,* but only within the last 

 few years has the connection between the two means of 

 securing energy been demonstrated. In addition to the ani- 

 mal and plant physiologists, our present knowledge is due 

 also to Pasteur and other bacteriologists, for they have 

 shown the peculiar habit of a large number of micro-organ- 

 isms in actively living only where free oxygen is absent. We 

 have a chain of allied processes : first, physiological oxida- 

 tion, or what may be called inter-molecular respiration, the 

 normal respiration of most organisms; second, physiologi- 

 cal rearrangement of atoms into simpler molecules, intra- 

 molecular respiration, the mode of respiration which many 

 cells and a good many organisms have recourse to under 



* Rollo. Annales de Chimie, t. 25, 1798. 



