38 APPLIED PHYSIOLOGY 



47. Difference between plants and animals. (i) The 



ability to live upon the ordinary waste products of animal life, or, in other 

 words, to reconstruct organic matter out of crude minerals and gases, is 

 a distinguishing mark of a plant. On the other hand an animal always 

 requires organic food, and cannot live upon the soil and air. Yet the 

 lowest animals very closely resemble plants, and owing to the difficulty 

 of ascertaining the true source of their food the position of some living 

 bodies is still a matter of dispute. 



(2) In animals the cells are bound together by strings of connective 

 tissue, which is an albuminous substance of soft consistency. In plants 

 the substance between the cells has the composition of starch (see 

 p. 27). It is a hard and firm substance, and gives the rigid strength to 

 the plant or tree. The outsides of the plant cells often have a thick 

 coating of the same substance. When it is deposited in so great an 

 amount as almost to replace the cells the substance forms wood. Yet 

 in some plants it is entirely absent, so that the distinction applies only 

 to higher forms of life, where other distinctions between plants and 

 animals are more obvious. 



(3) Most animals have the power of voluntary motion, while most 

 plants 2xe fixed to one spot. Yet some animals, as the coral, have no 

 more motion than a flower which opens and closes during the day. On 

 the other hand some water plants are continually moving about by 

 means of vibrating hairs projecting from their bodies. 



Some plants also move if irritated. The plant called Venus's flytrap 

 fias stiff, toothed leaves, hinged together in twos so as to open and shut 

 like a rat trap. When a fly alights upon the open leaf it suddenly closes 

 upon the insect, crushing it to death. This plant exhibits more move- 

 ment responsive to a slight irritation and directed to a distinct purpose 

 than many true animals. 



(4) Most animals have a digestive tube, while plants have no organs 

 of digestion, unless the leaves can be called such. Yet in some animals, 

 as the ameba, the body looks nearly the same throughout. 



(5) Most plants are green in color, from the presence of chlorophyll. 

 Yet many plants, as toadstools, are destitute of chlorophyll. 



48. Source of life. In the oxidation and reconstruction 

 of animals and plants no new life is created. Lifeless 

 material is endowed with life by material already living, 

 and in its turn the new material imparts life. The same 



