THE VITAL PHENOMENA OF CELLS 27 



1. The above-mentioned destruction in a majority of cases is an oxidation, 

 that is, a combustion of the substances called organic foodstuffs proteid, fat 

 and carbohydrate at the disposal of the cell (Lavoisier, 1777). This is 

 proved by the fact that all animals produce carbon dioxide, and that they 

 succumb in a short time in the absence of oxygen. Since a plant under the 

 influence of sunlight has the power to reduce carbon dioxide and set oxygen 

 free, it follows that under suitable circumstances plants and animals can live 

 if they be kept together in a closed room; for the carbon dioxide formed by 

 the animals is reduced by the plants with the liberation of oxygen; and thus 

 each receives the gas most useful in its life processes. 



And yet we are not to suppose that the plant does not form any carbon 

 dioxide. On the contrary the plant protoplasm in its production of kinetic 

 energy behaves exactly like the animal protoplasm and produces carbon dioxide 

 in the same way. The production of carbon dioxide in green plants in the 

 light is masked by the much more abundant reduction of carbon dioxide going 

 on at the same time; in the dark, however, where the reduction processes are 

 checked, it is plainly perceptible. 



In the decomposition brought about by the vital activity the combustible 

 substances are not broken down immediately into their end products ; but the 

 complex organic molecules are split up gradually into less and less complex 

 ones, oxidation and reduction processes probably taking place in rapid suc- 

 cession (Drechsel). Finally, these intermediate decomposition products are 

 transformed into substances which leave the body as the end products of 

 metabolism. 



2. The living cell itself regulates the amount of oxygen consumed, combus- 

 tion in the body being, within wide limits, entirely independent of the partial 

 pressure of the uncombined oxygen (Pfliiger). 



In addition protoplasm has the power to store up oxygen in compounds in 

 which it is loosely held, and from which it may be withdrawn again in case of 

 need. This is witnessed by the fact that cells can develop kinetic energy, 

 though in general only for a relatively short time, without a supply of free 

 oxygen from outside. In certain cases this happens even at the expense of 

 compounds which contain oxygen firmly bound up chemically and which cannot 

 be deoxidized with our strongest reducing agents. We have examples of such 

 phenomena in the Myxomycetes which continue their movements for three hours 

 in an oxygen-free medium; in ciliated cells which can live still longer without 

 oxygen; in the skeletal muscles which contract and give off carbon dioxide even 

 in a vacuum. The mawworm, Ascaris, can live five days without a supply of 

 oxygen (Bunge). In this case there occurs in the body of the animal a process 

 of fermentation by which CO 2 and a mixture of valerianic acid, caproic acid, 

 etc., are formed from the glycogen stored in the animal's tissues (Weinland). 

 Here should be mentioned also the liberation of oxygen by hen's eggs during the 

 first five hours of their incubation (Hasselbalch). 



A very pretty experiment on the life of higher animals in the absence of 

 oxygen is the following which we owe to Pfliiger. At 2.44 o'clock two frogs 

 were placed in an atmosphere cooled to about C. from which every trace of 

 oxygen had been carefully removed. At three o'clock they showed the most 

 pronounced dyspnoea but no convulsions. They soon became motionless, as if 

 they wished by suppression of their movements to obviate the need for oxygen. 



