RESPIRATION 37 



respiration, fermentation, decay, and disease, attacking the 

 same complex compounds first, result in the formation of 

 the same simple ones finally. This is done only slowly, 

 through many stages, with the same total of released 

 energy, but with far less energy available for the individual 

 organisms in the long chain. Thus the energy stored in the 

 compounds elaborated by living organisms is set free again 

 before and after their death, either by their own activity or 

 by the activity of others. This energy becomes available 

 for the construction of new energy-storing compounds, for 

 work of the utmost physiological variety. 



From the foregoing discussion it is evident that respira- 

 tion, whether aerobic or anaerobic, is a process most inti- 

 mately connected with the other functions of the living 

 organism; a process dependent in the first place upon a 

 supply of respirable (oxidizable or otherwise decomposable) 

 material; a process which goes on, when once respirable 

 material is adequately supplied, actively or tardily, accord- 

 ing to the activity of the other functions, in other words, 

 according to the demand for energy to do work. In the 

 healthy organism, under natural conditions, the rate of 

 respiration will equal the demand for energy; it will not 

 exceed the demand, for stimulating respiration results in 

 stimulating the other activities ; it will not be less than the 

 demand, for decreasing respiration decreases the amount of 

 energy available for the other activities. The rate of res- 

 piration is controlled by the living cell, and whatever in- 

 fluences affect the total amount of energy demanded by it 

 will also affect the rate of respiration, increasing or de- 

 pressing the rate accordingly. 



Respiration lias no optimum temperature, no optimum 

 illumination, of its own: it will increase or decrease with 

 changes in temperature and illumination only as these affect 

 the demand for energy on the part of the organism. Nutri- 

 ent and poisonous substances and the amount of water will 

 affect respiration only as they affect the organism. Injuries* 

 cause a change in the rate of respiration, but they do so 



* Richards, H. M. The respiration of wounded plants. Annals of Bot- 

 any, Vol. X., 1896. 



