12 THE PHENOMENA OF LIFE 



bodies out of very simple chemical substances obtained from the air and from 

 the soil. They obtain from the air oxygen, carbon dioxide, and water, as 

 well as traces of ammonia gas; and from the soil they obtain water, ammonium 

 salts, nitrates, sulphates, and phosphates in combination with such bases as 

 potassium, calcium, magnesium, sodium, iron, and others. The majority 

 of plants are able to work up these elementary compounds into other and more 

 complicated bodies. This they are able to do in consequence of their contain- 

 ing a certain coloring matter called chlorophyll, the presence of which is the 

 cause of the green hue of plants. In all plants which contain chlorophyll two 

 processes are constantly going on when they are exposed to light: one, which 

 is called true respiration and is a process common to animal and vegetable 

 cells alike, consists in the taking of the oxygen from the atmosphere and the 

 giving out of carbon dioxide; the other, which is peculiar apparently to bodies 

 containing chlorophyll, consists in the taking in of carbon dioxide and the 

 giving out of oxygen. It seems that the chlorophyll is capable of decomposing 

 the carbon dioxide gas and of fixing the carbon in the structures in the form of 

 new compounds, one of the most rapidly formed of which is starch. 



Vegetable protoplasm by the aid of its chlorophyll is able to build up a large 

 number of bodies besides starch, the most interesting and important being 

 proteid or albumin. It appears to be a fact that the power which bodies pos- 

 sess of being able to synthesize is to a large extent dependent upon the chloro- 

 phyll they contain. Thus the power is present to a marked extent only in the 

 plants in which chlorophyll is found, and is absent in those which do not 

 possess it. It is probably present only in slight degree as one of the proper- 

 ties of animal protoplasm. 



It must be recollected, however, that chlorophyll without the aid of the 

 light of the sun can do nothing in the way of building up substances, and a 

 plant containing chlorophyll when placed in the dark, while it continues to live, 

 and that is not as a rule long, acts as though it did not contain any of that sub- 

 stance. It is an interesting fact that certain of the bacteria have the chlorophyll 

 replaced by a similar pigment which is able to decompose carbon dioxide gas. 



Animal cells do not possess the power of building up or synthesizing from 

 simple materials; their activity is chiefly exercised in the opposite direction, 

 viz., they have brought to them as food the complicated compounds produced 

 by the vegetable kingdom. With these foods they are able to perform their 

 complex functions, setting free energy in the direction of heat, motion, and 

 electricity, and at the same time eliminating such bodies as carbon dioxide and 

 water, and producing other bodies, many of which contain nitrogen, but are 

 derived from decomposition. 



With reference to the substance chlorophyll it is necessary to say a few 

 words. It has been noted that the synthetical operations of vegetable cells are 

 peculiarly associated with the possession of chlorophyll and that these opera- 

 tions are dependent upon the light of the sun. It has been further shown that 



