16 INTRODUCTION. 



SUMMARY IDKA OF THE FUNCTIONS AND ORGANS OF THE BODIES OF 

 ANIMALS, AND OF THEIR VARIOUS DEGREES OF COMPLICATION. 



After what we have stated respecting the organic elements of the 

 body, its chemical principles and acting powers, nothing remains but 

 to give a summary idea of the functions of which life is composed, and 

 of their appropriate organs. 



The functions of the animal body are divided into two classes : 



The animal functions, or those proper to animals, that is to say, 

 sensibility and voluntary motion. 



The vital, vegetable functions, or those common to animals and 

 vegetables, that is, nutrition and generation. 



Sensibility resides in the nervous system. 



The most general external sense is that of touch ; it is seated in the 

 skin, a membrane that envelopes the whole body, which is traversed in 

 every direction by nerves whose extreme filaments expand on the 

 surface into papillae, and are protected by the epidermis and other 

 insensible teguments, such as hairs, scales, &c. &c. Taste and smell 

 are merely delicate states of the sense of touch, for which the skin of 

 the mouth and nostrils is particularly organised : the first, by means 

 of papillae more convex and spongy ; the second, by its extreme 

 delicacy and the multiplication of its ever humid surface. We have 

 already spoken of the ear and the eye. In fine, sensations more or less 

 painful may originate in every part of the body through accident or 

 disease. 



Many animals have neither ears nor nostrils ; several are without eyes, 

 and some are reduced to the single sense of touch, which is never absent. 



The action received by the external organs is continued by the nerves 

 to the central masses of the nervous system, which, in the higher 

 animals, consists of the brain and the spinal marrow. The more ele- 

 vated the nature of the animal, the more voluminous is the brain and the 

 more is the sensitive power concentrated there; the lower the animal, 

 the more medullary masses are dispersed, and in the most imperfect 

 genera, the entire nervous substance seems to melt into the general 

 matter of the body. 



That part of the body, which contains the brain and principal organs 

 of sense, is called the head. 



When the animal has received a sensation, and this has occasioned 

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

 the muscles. 



