130 THE CELL 



in which active streaming protoplasmic movements are taking 

 place, are immersed in a drop of pure olive oil, the movements, in 

 consequence of the exclusion of the oxygen, soon commence to 

 slacken, and finally quite cease. The same occurs when plant- 

 cells are introduced into an atmosphere consisting exclusively of 

 carbon dioxide or of hydrogen, or of a mixture of the two. At 

 first the functions of the protoplasm are only arrested, and if the 

 olive oil, carbon dioxide, or hydrogen, be soon removed, the irrita- 

 bility and movements return gradually after a period of rest. If 

 however the cells are deprived of oxygen for a considerable time, 

 their functions become paralysed, until finally death, accompanied 

 by the turbidity, coagulation, and decomposition of the protoplasm, 

 ensues. 



In a similar manner each animal cell respires. If a hen's egg, 

 which has been incubated, and which, being in an early stage of 

 development, consists simply of small cells, is placed in an atmos- 

 phere of carbon dioxide, or if its porous shell is so saturated 

 with oil that no interchange of gases can take place between the 

 embryo and the outer air, the egg dies in a few hours. 



The oxygen which is absorbed by man through the lungs serves 

 to satisfy the need of oxygen evinced by all the cells contained in 

 the various tissues of our bodies. This last process is designated 

 in animal physiology internal or tissue respiration, in contradis- 

 tinction to the taking in of oxygen or lung respiration. 



In the ivhole organic kingdom, respiration is united ivith the excre- 

 tion of carbon dioxide and with the production of heat. The follow- 

 ing is a simple chemical law : " A certain amount of heat is 

 evolved during respiration, just as it is produced in every other 

 case when carbon and hydrogen are oxidised into carbon dioxide 

 and water " (Sachs IV. 32a). Plant cells expire carbon dioxide 

 and evolve heat, just like animal cells. 



The formation of heat is most easily demonstrated in portions 

 of plants which are growing rapidly ; such as in germinating 

 seeds. It can be especially well detected in the flowers of Aroidese. 

 These become heated to as much as 15 C. above the temperature 

 of their surroundings. 



The living cell itself is able, by means of its respiration, to 

 regulate the amount of oxygen which it consumes. This depends 

 simply upon the degree of its functional activity, to which the 

 decomposition of organic substance is proportionate. An unfer- 

 tilised egg-cell and a resting plant seed breathe in very minute 



