202 LECTURE XI. 



We may briefly mention here that the inorganic sub- 

 stances which are absorbed by a plant may materially 

 affect its respiration. Kellner has observed, for instance, 

 that when germinating seeds were supplied with potassium 

 nitrate, they absorbed it, and they exhaled considerably more 

 carbon dioxide than others which were not supplied with 

 the salt. He concludes that the oxygen which would be set 

 free in the plant in consequence of the reduction of the ab- 

 sorbed nitric acid serves to promote oxidation and thereby 

 the exhalation of carbon dioxide as well. 



He determined the relative amounts of carbon dioxide exhaled to be 

 as follows : 



10 grammes of peas in distilled water in solution of KNO 3 . 



Exhaled in 5 days 0*3869 0-4296 grm. CO 2 . 



The peas in the splution of KNO 3 absorbed o'io68 gramme N 2 O 5 . 



It must be remarked, however, that Kellner's results are 

 not conclusive as regards the effect of the oxygen contained 

 in the nitric acid. It is quite possible that the effect of the 

 salt may have been to promote the metabolic activity of the 

 seeds including the absorption of oxygen from the air. 



We have now to endeavour to ascertain what is the re- 

 lation of the absorbed oxygen and of the evolved carbon 

 dioxide to the metabolic processes, and we will begin with 

 the self-decomposition of the protoplasm. We may, at the 

 outset, make the general statement that the continual ab- 

 sorption of oxygen is essential to the existence of living 

 organisms (with certain exceptions which we shall notice 

 hereafter), and that in the absence of such a supply of oxygen 

 they cease, within a longer or a shorter time, to exhibit those 

 phenomena in virtue of which we call them living, in a word, 

 they die. Death under these circumstances is to be attributed 

 to the arrest of the metabolic processes which are accompanied 

 by the evolution of energy in the organism, and of these 

 by far the most important is the self-decomposition of the 

 protoplasm. It appears, then, that the absorption of oxygen 

 is essential to the self-decomposition of the protoplasm- 

 mole.ciile. It is of course impossible to make any final state- 



