54 THE VITAL FUNCTIONS. 



that nothing which can afford nutriment is wholly 

 lost. There is no part of the organized structure of 

 an animal or vegetable, however dense its texture, 

 or acrid its qualities, that may not, under certain 

 circumstances, become the food of some species of 

 insect, or contribute in some mode to the support 

 of animal life. The more succulent parts of plants, 

 such as the leaves, or softer stems, are the principal 

 sources of nourishment to the greater number of 

 larger quadrupeds, to multitudes of insects, as well 

 as to numerous tribes of other animals. Some 

 plants are more particularly designed as the ap- 

 propriate nutriment of particular species, which 

 would perish if these ceased to grow : thus the silk- 

 worm subsists almost exclusively upon the leaves 

 of the mulberry tree ; and many species of cater- 

 pillars are respectively attached to a particular 

 plant, which they prefer to all others. There are 

 at least fifty different species of insects that feed 

 upon the common nettle ; and plants, of which the 

 juices are most acrid and poisonous to the gene- 

 rality of animals, such as Euphorhium, Henbane^ 

 and Nightshade, afford a wholesome afid delicious 

 food to others. Innumerable tribes of animals sub- 

 sist upon fruits and seeds ; w hile others feast upon 

 the juices which they extract from flowers, or other 

 parts of plants ; and others, again, derive their 

 principal nourishment from the hard fibres of the 

 bark or wood. 



Still more general is the consumption of animal 

 matter by various animals. Every class has its 

 carnivorous tribes, which consume Uving prey of 

 every denomination ; some being formed to devour 

 the flesh of the larger species, whether quadrupeds, 



