THE VITAL PROPERTIES OF THE CELL 133 



they can be shown by chemical analysis to consist chiefly of oxy- 

 gen. The amount of oxygen exhaled is in proportion to the carbon 

 dioxide which is simultaneously absorbed out of the water, and the 

 carbon of which is elaborated into carbo-hydrates. It has already 

 been mentioned in a, previous chapter (p. 103), that the living 

 protoplasm, which is sensitive to light, endeavours to bring the 

 chlorophyll corpuscles into favourable positions for receiving the 

 direct powerful rays of light. 



The process of assimilation proceeds in such an energetic man- 

 ner under the influence of sunlight that, in comparison to it, the 

 respiration of oxygen and the exhalation of carbon dioxide, which 

 are absolutely essential for the maintenance of the vital processes, 

 are placed quite in the background, so much so, indeed, that in 

 former times they were quite overlooked. But in plants which 

 are placed in the dark, the expiration of oxygen and, to an equal 

 degree, the absorption of carbon dioxide are immediately arrested, 

 whilst respiration continues in precisely the same manner as when 

 the plants were in the light. The gas now given off is seen to be 

 carbon dioxide, the quantity of which, however, is much less than 

 that of the oxygen in the preceding experiment. 



Claude Bernard (IV. la) has drawn attention to a very interest- 

 ing difference existing between the respiration of oxygen and the 

 assimilation of carbon dioxide in plants. He narcotised water- 

 plants by means of chloroform or ether, and then found that they 

 no longer gave off oxygen in direct sunlight. Thus the function 

 of the chlorophyll, the capacity of forming starch by synthesis 

 from carbon dioxide and water, is absolutely suspended during 

 narcosis, just as the irritability and power of motion are arrested 

 in the protoplasm. This capacity returns when the plants are 

 transferred into pure water. But it is still more remarkable that 

 respiration, including the exhalation of carbon dioxide, is uninter- 

 rupted during narcosis. This difference may be probably traced 

 back to the fact that respiration, and the decomposition in connection 

 with it, stand in a much closer relationship to the whole vital eco- 

 nomy, and hence can only be quite extinguished with the life of 

 the cell itself. But long before this occurs, the functions of the 

 cell are paralysed during narcosis, and with them the chlorophyll 

 function. 



2. The Absorption and Excretion of Fluid Substances. Most of 

 the substances concerned in metabolism are taken up by the organ- 

 ism in a fluid condition. Unicellular and aquatic plants extract 



