24 THE BODY AT WORK 



of the substances which the sun's rays enable the plant 

 to make. A plant, equally with an animal, respires. 

 The distinction between the constructive metabolism 

 of a plant and its respiration may be brought out in a 

 striking way by administering to it sufficient anaesthetic to stop 

 the former without stopping the latter. It may be paralyzed 

 without being killed. If a water-weed potamogeton is the 

 most convenient enclosed in a bell-glass filled with water 

 and inverted over a dish of water, is placed in sunshine, 

 bubbles of gas rise from the plant. They accumulate at the top 

 of the bell-glass. If the gas be removed and analysed, it is 

 found to be oxygen with a small admixture of carbonic acid. If 

 a second bell-glass containing water-weed be exposed under 

 the same conditions in all respects, save that a small quantity 

 of chloroform is added to the water, the gas that collects at 

 the top of the bell- jar will be much less in amount. It will 

 be found to be carbonic acid without admixture of oxygen. 

 The power which chlorophyll possesses of decomposing carbonic 

 acid with fixation of carbon and liberation of oxgyen is 

 suspended by the anaesthetic ; whereas respiration is not inter- 

 fered with. 



Lastly, we must attribute to protoplasm a capacity of grow- 

 ing. The activity of protoplasm depends upon constant mole- 

 cular interchange. It incorporates molecules of food. It 

 excorporates molecules of waste. If food is abundant and 

 " vitality " exuberant, it takes in more than it gives out. 

 It grows. 



If we attempt to formulate a definition of protoplasm, we 

 find that our ideas are far from clear, owing to want of know- 

 ledge. The questions, What is protoplasm ? What is life ? 

 are equally unanswerable. Their definition is reciprocal. 

 Protoplasm is the substance, the material, which exhibits life. 

 Life is the complex of phenomena exhibited by protoplasm. 

 All parts of the body are alive, in their degree. The nucleus of 

 a cell lives, as well as its cell-body. Its capsule may be less 

 alive that is to say, less vibrant than the soft cell-substance 

 which it encloses ; but it lives. So-called intercellular sub- 

 stance, or matrix, is alive. In growing cartilage the matrix 

 does not behave as a dead substance. It does not crack and 

 gape under the pressure of the dividing and multiplying cell- 



