90 THE NrTRITIVE FUNCTIONS. 



much importance as a moistened soil. House-plants fre- 

 quently suffer from the dust with which their leaves become 

 covered. Their health and general appearance may be 

 very much improved^ by a careful cleansing of theiy leaves 

 every other day, with a wet sponge. It is as important to 

 keep the epidermis of a plant in a cleanly state as the sMn 

 of an animal. Neglect in either instance brings on disease, 

 premature decay, and loss of vitality. 



The food of animals is not furnished to them in a 

 condition fit for assimilation and circulation. It comes into 

 contact with their organs in a more or less solid state, and 

 a cavity is therefore provided in the interior of their 

 organism for its reception, and reduction to a condition fit 

 to enter the circulation. 



We have seen that one of the most striking differences 

 between animals and plants is the possession by the former 

 of a nervous system of which the latter are totally deprived. 

 This nervous system is the seat of all the sensations and 

 movements of animal life. It manifests itself in the un- 

 erring instincts of inferior creatures, enabling them to pro- 

 cure themselves food and defend themselves against their 

 enemies, and in those higher attributes of reason and reflec- 

 tion which appear gradually in the lower animals, and 

 obtain in man, " the minister and interpreter of nature," 

 their noblest and most exalted expression. Creatures thus 

 endowed must provide food for themselves. It comes to 

 them no more mechanically and chemically. 



Thus, at the very outset, the nutritive apparatus of 

 animals is much more complicated than that of plants. 

 Their food has to be both procured and prepared by them- 

 selves, before it can be assimilated. They are provided 

 with senses and appropriate organs for this very purpose, 

 and they must exercise* both if they would obtain the 



