RESPIRATION 29 



favorable periods, and those for which anaerobic respiration 

 is similarly and equally indispensable, there are all connect- 

 ing stages. These are found among the lower plants, es- 

 pecially among the fungi ; but, as before stated, in all large 

 multicellular organisms, especially among animals, there are 

 probably cells, Ijang deep in the tissues, which are forced 

 by the positions they occupy to supply themselves with 

 needed kinetic energy by the same means as the anaerobic 

 organisms, namely, by decomposing the complex compounds 

 which they contain. There are, then, cells as well as or- 

 ganisms which are obligate aerobic, facultative aerobic, and 

 obligate anaerobic. The obligate anaerobic cells and or- 

 ganisms live where the access of free oxygen is impossible or 

 difficult : for instance, deep in living tissues, either as com- 

 ponent parts of these tissues, or as parasites and sapro- 

 phytes 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 ; indeed, wherever 

 there are proper food, proper temperature, and proper 

 freedom. 



As in aerobic so also in anaerobic respiration, other 

 processes take place simultaneously with it. These, if not 

 directly caused by respiration, are at all events main- 

 tained by the energy liberated in it, and are so closely 

 connected with it that to distinguish between the chemical 

 products of respiration and those of the processes accom- 

 panying it, is a matter exceedingly difficult and not yet 

 fully accomplished. Fermentation, decay, and disease at 

 least accompany, if they are not actually a part of, the 

 respiratory processes of certain low plants. Anaerobic respi- 

 ration, as well as aerobic, is a function of the living pro- 

 toplasm, which acts upon substances 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 entirely inactive chemically, like carbon-diox- 

 ide and alcohol; others may act upon the substances out- 

 side of the cell. In the higher animals and plants the enzyms 

 ( like pepsin, diastase, etc. ) are produced in connection with 

 the process of nutrition, converting the substances upon 



