THE VITAL PROPERTIES OF THE CELL 131 



quantities of oxygen ; however, after the egg-cell has been fer- 

 tilised, and division is proceeding rapidly, or when the plant seed 

 germinates, the amount of oxygen which is absorbed increases. 

 This absorption of oxygen is one of the functions of active living 

 protoplasm (Sachs). Thus the following is easily explained, that 

 the absorption of oxygen by the living cell " is, within certain 

 wide limits, quite independent of the gaseous tension of the 

 oxygen" (Pfliiger). 



One important phenomenon must be described before closing 

 this chapter on respiration. Even when oxygen is absent the cells 

 are able to excrete carbon dioxide and evolve heat for a longer or 

 shorter time. If germinating plants are introduced into a 

 Torricellian vacuum, they continue to exhale a normal quantity of 

 carbon dioxide for about an hour, after which the quantity gradu- 

 ally decreases. 



According to Pfliiger's experiments, Frogs can live for several 

 hours in a bell-jar which is free from oxygen and filled with 

 nitrogen, during which time they exhale a considerable quantity 

 of carbon dioxide. 



Both these experiments prove, that for a time, without direct 

 access to oxygen, but simply through the decomposition of organic 

 substances, carbon and oxygen atoms may unite together in the 

 cell to form carbon dioxide. 



This process is termed intramolecular respiration. As long as 

 this persists, the cell lives, and remains irritable and capable of 

 performing its functions, although with continually decreasing- 

 energy, by using up a portion of the oxygen contained in combina- 

 tion in its substance. However, when oxygen is withheld for a, 

 considerable time, death invariably ensues. 



Upon these phenomena of intramolecular respiration the pro- 

 position already mentioned rests : " that the first impulse to the 

 chemical processes of respiration is not given by the oxygen 

 which enters from without, but that first and primarily a decom- 

 position of albumen molecules resulting in the formation of carbon 

 dioxide takes place inside the protoplasm, and that hence the 

 incoming oxygen effects a restitutio in integrum." 



In fermentation processes, during which the ferments grow, multiply, and 

 evolve carbon dioxide, without having access to oxygen, we see an instance 

 which resembles intramolecular respiration ; to this Pfeffer (V. 22) has called 

 especial attention. 



