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 tc 

 the peculiar habits of some of the lowest organisms, thes< 

 are obliged to obtain needed energy in this way and hav< 

 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 it 

 not explicitly descriptive. The German term SpaltungsatL 

 mung is in this regard much more satisfactory, but it is nol 

 concisely translatable. Ordinary respiration, physiologica 

 oxidation or physiological combustion, is aerobic respira 

 tion respiration which is dependent upon free oxygen, anc 

 which yields the needed kinetic energy only by the union o 

 free oxygen with combustible substances. Intramoleculai 

 respiration, physiological simplification of complex sub 

 stances, physiological rearrangement of atoms, is anaerobic 

 respiration respiration which takes place only when fre< 

 oxygen is present in insufficient quantities or is altogethei 

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

 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 intramoleculai 

 respiration was first observed,* but only within the lasl 

 few years has the connection between the two means o 

 securing energy been demonstrated. In addition to the ani 

 mal and plant physiologists, our present knowledge is du< 

 also to Pasteur and other bacteriologists, for they hav< 

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

 isms in actively living only where free oxygen is absent. W< 

 have a chain of allied processes : first, physiological oxida 

 tion, or what may be called inter-molecular respiration, th( 

 normal respiration of most organisms; second, physiologi- 

 cal rearrangement of atoms into simpler molecules, intra 

 molecular respiration, the mode of respiration which man} 

 cells and a good many organisms have recourse to undei 



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



