"Cuvierian System of Zoology. 99 



food of animals, either mediately * or directly, is derived from 

 vegetables, in which hydrogen and carbon are the principal 

 constituent parts. To reduce them to their proper composition, 

 it is necessary that the excess of hydrogen, and more particu- 

 larly of carbon, should be diminished, and that the quantity of 

 azote should be increased ; this is effected, in respiration, by the 

 oxygen of the atmosphere, which combines with the hydrogen 

 and carbon of the blood, and is exhaled with them in the state 

 of water, or carbonic acid. The azote, from whatever part it 

 may enter the animal body, appears to remain there. The 

 relations of vegetables and animals with the atmosphere are, 

 therefore, the reverse of each other ; vegetables extract and de- 

 compose (defont) water and carbonic acid, animals reproduce 

 them. Respiration is the function essential to the constitution 

 of the animal body ; it is what, in some manner, animates it, 

 and we shall see, as we proceed, that the animal functions are 

 more or less completely exerted, as the animals enjoy a more 

 or less complete respiration ; the difference in this respect forms 

 the fourth character of animals. 



The functions of the animal body are divided into two 

 classes : 1st, The animal fujictions^ or those peculiar to animals, 

 which are sensibility and voluntary motion ; 2d, The vital or 

 vegetative functions, common to animals and vegetables, which 

 are nutrition and generation. Sensibility resides in the ner- 

 vous system. The most general of the external senses is the 

 feeling; it resides in the membrane that covers the whole 

 body, called the skin. Many animals are without ears or 

 nostrils ; several animals have no eyes ; some are reduced to 

 the single sense of feeling ; but this sense is possessed by all 

 animals. The impressions received by the external senses, are 

 propagated by the nerves to the central masses of the nervous 

 system, which, in the higher classes of animals, consist of a 

 brain and spinal chord. In proportion as animals partake of 

 a superior nature, the brain is larger, and sensation is more 

 concentrated in this organ ; and in proportion as they are placed 

 lower in the scale, the medullary masses are dispersed. In the 

 most imperfect genera the nervous substance appears to be 

 entirely diffused in the general substance of the body. When 

 an animal has received a sensation, and a volition is excited, 

 it is by the nerves that this volition is transmitted to the 

 muscles. The muscles are bundles [faisceaux) of fleshy fibres, 

 whose contractions produce all the motions of the animal body. 

 The number and direction of the muscles of every animal are 



* Carnivorous animals prey on those which derive their food from the 

 vegetable kingdom. 



H 2 



