DIFFERENCES BETWEEN ANIMALS AND PLANTS 13 



a solution of chlorophyll has a definite absorption spectrum when examined 

 with the spectroscope, and that it is particularly those parts of the solar spec- 

 trum corresponding to these absorption bands which are chiefly active in the 

 decomposition of carbon dioxide. In the synthetical processes of the plant 

 then, by aid of its chlorophyll, the radiant energy of the sun's rays becomes 

 stored up or rendered potential in the chemical products formed. The poten- 

 tial energy is set free, or is again made kinetic, when these products simply by 

 combustion produce heat, or when they are taken into the animal organism 

 and used as food and to produce heat and motion. 



The influence of light is not an absolute essential to animal life; indeed, it 

 is said not to increase the metabolism of animal tissue to any great extent, 

 and the animal cell does not receive its energy directly from the sun's light, 

 nor yet to any extent from the sun's heat, but from the potential energy of the 

 food stuffs. But it must be always kept in mind that anabolism is not peculiar 

 to vegetable, or katabolism to animal cells; both processes go on in each. 

 Some of the lowest forms of vegetable life, e.g., the bacteria, will live only in a 

 highly albuminous medium, and in fact seem to require for their growth 

 elements of food stuffs which are essential to animal life. In their metabolism, 

 too, they very closely approximate animal cells, not only requiring an atmos- 

 phere of oxygen, but giving out carbon dioxide freely, and secreting and excret- 

 ing many very complicated nitrogenous bodies, as well as forming proteid, 

 carbohydrates, and fat, requiring heat but not light for the due performance 

 of their functions. Certain bacteria grow only in the absence of oxygen. 



There is, commonly, a difference in general chemical composition between 

 vegetables and animals, even in their lowest forms; for associated with the 

 protoplasm of the former is a considerable amount of cellulose, a substance 

 closely allied to starch and containing carbon, hydrogen, and oxygen only. 

 The presence of cellulose in animals is much rarer than in vegetables, but there 

 are many animals in which traces of it may be discovered, and some in which 

 it is found in considerable quantity. The presence of starch in vegetable cells 

 is very characteristic, though, as we have seen above, it is not distinctive, and 

 a substance, glycogen, similar in composition to starch, is very common in the 

 organs and tissues of animals. 



Inherent power of movement is a quality which we so commonly consider 

 an essential indication of animal nature that it is difficult at first to conceive of 

 its existence in any other. The capability of simple motion is now known, 

 however, to exist in so many vegetable forms that it can no longer be held 

 as an essential distinction between them and animals, and ceases to be a mark 

 by which the one can be distinguished from the other. Thus the zoospores of 

 many of the Cryptogams exhibit ciliary or ameboid movements of a like 

 kind to those seen in amebae; and even among the higher orders of plants, 

 many, e.g., Dioncza muscipula ( Venus J s fly-trap), and Mimosa sensitive, (Sensi- 

 tive plant) exhibit such motion, either at regular times or on the applica- 



