Unicellular and Multicellular Animals 



been described as a condition of ' chronic indecision/ neither 

 clearly vegetable nor definitely animal. But very soon, in the 

 march of progress, the forking of the 

 roads was reached, and whosoever 

 was bent on journeying farther had 

 perforce to make the choice. We 

 must here briefly consider what this 

 choice was, and wherein the funda- 

 mental distinction between a plant 

 and an animal consists ; for, strange 

 as the statement may seem, the basis 

 of this distinction is by no means 

 generally appreciated. 



The typical plant lives by absorb- 

 ing carbon dioxide gas, water, and 

 mineral salts from the surrounding media. These substances, 

 by means of energy which it gathers from the rays of the sun, 

 the plant builds up into organic substances, to be used in the 



maintenance of life, 

 and for growth and 

 reproduction. This 

 process of chemical 

 construction occurs 



FIG. 19. The bacillus of bubonic 

 plague (x 1000). 



Photo : F. Martin Duncan. 



only in the green, 



% 4fc * % ^% exposed parts of the 



j^ " I plant, and indeed can 



Tm^** 9^^ I occur only in the pre- 



jf^^tTI , ' j* ' sence of chlorophyll, 



J^^ w \ the green colouring 



mi < matter of the leaves. 



* ^ * | The animal, on the 



other hand, lives by 

 appropriating, either 

 directly or indirectly, what the plant has produced. All flesh is 

 indeed grass, in a different sense from that originally intended by 

 the statement. It is this essential difference which lies at the 



29 



FlG. 20. The bacillus of typhoid (x 2500 diameteis). 



Photo : F. Martin Duncan. 



