Amongst the chemical phenomena of life is respiration. =Respiration= in this very general sense means oxidation. The force which is exhibited in living is obtained from the union of organic materials with oxygen under the direction of protoplasm. This is true of plants as well as of animals. It is true even of the subdivision of bacteria, termed anaerobic, because they cannot live in air. They secrete ferments which enable them to decompose compounds which contain oxygen, in order that they may use the oxygen for respiration. It might have been supposed that green plants which are receiving radiant energy from the sun would convert this energy into the forces which enable protoplasm to display the phenomena of life. But this is not so. The energy which green plants obtain from the sun is used in constructive metabolism, and not in maintaining life. Life-force, if we may use the expression, is derived from the oxidation 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 anæsthetic 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 oxygen is suspended by the anæsthetic; whereas respiration is not interfered with.
Lastly, we must attribute to protoplasm a =capacity of growing=. The activity of protoplasm depends upon constant molecular 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.