THE PHENOMENA OF LIFE 



Dilute salt-solution and many dilute acids and alkalies stimulate the move- 

 ments temporarily. Strong acids or alkalies permanently stop the movements; 

 ether, chloroform, veratrium, and quinine also stop it for a time. 



Movement is suspended in an atmosphere of hydrogen or carbonic acid 

 and resumed on the admission of air or oxygen, but complete withdrawal of 

 oxygen will after a time kill the protoplasm. 



e. Electrical. Weak currents stimulate movement, while strong currents 

 cause the cells to assume a spherical form and to become motionless. 



The Power of Digestion, Respiration, and Nutrition. This consists in the 

 power which is possessed by the ameba and similar animal cells of taking in 

 food, modifying it, building up tissue by assimilating it, and rejecting what is 

 not assimilated. These various processes are effected in some one-celled ani- 

 mals by the protoplasm simply flowing around and enclosing within itself 

 minute organisms such as diatoms and the like. From these it extracts what 

 it requires, and then rejects or excretes the remainder, which has never formed 

 part of the body. This latter proceeding is done by the cell withdrawing 

 itself from the material to be excreted. The assimilation constantly taking 



place in the body of the ameba is for the pur- 

 pose of replacing waste of its tissue consequent 

 upon manifestation of energy. The respiratory 

 process of absorbing oxygen goes on at the same 

 time. 



The processes which take place in cells, 

 both animal and vegetable, are summed up 

 under the term metabolism (from peTafioty, 

 change). The changes which go on are of two 

 kinds, viz., assimilation, or building up, and 

 disassimilation, or breaking down ; they may 

 be also called, using the nomenclature of Gas- 

 kell, anabolism or constructive metabolism, and 

 catabolism or destructive metabolism. In the 

 direction of anabolism two processes occur, 

 viz., the building up of materials which it 

 takes in, and secondly, the building up of its 

 own substance by those or other materials. 

 As we shall see in a subsequent paragraph, 

 the process of anabolism differs to some ex- 

 tent in vegetable and animal cells. The catab- 

 olism of the cell consists in chemical changes which occur in the cell- 

 substance itself, or in substances in contact with it. 



The destructive metabolism of a cell is increased by its activity, but goes 

 on also during quiescence. It is probably of the nature of oxidation, and re- 

 sults in the evolution of carbon dioxide and water on the one hand, and in the 



FIG. 6. Cells from the Staminal 

 Hairs of Tradescantia. A, Fresh 

 in water; B, the same cell after 

 slight electrical stimulation; a, b, 

 region stimulation; c, d, clumps 

 and knobs of contracted proto- 

 plasm. (KUhne.) 



