useful or injurious to him ; motion, by enabling him to approach, or 

 avoid such objects, according; as he perceives relations of advantage or 

 disadvantage, according as the opposite sensations of pain or pleasure re- 

 sult from his action on them, or from theirs on him. In fine, voice and 

 speech give him communication with beings enjoying the same means of 

 communication, and that without a necessity of motion. The brain is the 

 principal organ of these functions, as thesystem of circulation is the cen- 

 tre of the assimilating functions. All the impressions received by the 

 organs of sense are transmitted to the brain, and from the brain, determi- 

 nations arise, as well as the voluntary motions and the voice. The san- 

 guineous system receives the molecules destined to nutrition, and those 

 which are to be thrown out of the body. The sensitive and circulatory 

 systems are the only systems provided with a centre, (the brain and the 

 heart) which extend to all parts of the body, by emanations originating 

 from that organ, or terminating in it (the nerves, the arteries, and veins,): 

 and, as the motions and the voice depend on sensation, and are immedi- 

 ately connected with it as necessary consequences, so, respiration, secre- 

 tion, and nutrition, are, in a manner, but consequences of the circulation 

 which distributes the blood to all the organs, in order that these may 

 produce on it various changes which constitute respiration., secretion and 

 nutrition. They are, to anticipate what is to come hereafter, only differ- 

 ent kinds of secretion that take place at the expense of the different prin- 

 ciples contained in the blood. 



The circulation which holds the functions of nutrition in a kind of de- 

 pendence, subjects the brain, which is the principal organ of the external 

 functions, to an influence still more immediate and indispensable. The 

 muscular motions are not less under its influence. It is the first function 

 that is apparent in the embryo, whose evolution it brings about; in natu- 

 ral death, of all the functions, it is the last to cease. There are many 

 reasons which justify Haller, for having placed it in the first order, and 

 for having begun by its history, his great work on physiology. I enter 

 into this digression, only to expose the absurdity of the claims of some 

 authors, who, because they have varied the methodical order of the func- 

 tions, broken the series, or made the slightest changes for example, by 

 placing the history of the function of smell and taste before the account 

 of the internal or nutritive functions, think they have totally changed the 

 aspect of the science: pitiful sophists, who accumulate subleties instead 

 of facts and ideas. 



In warm and red-blooded animals, the nutritive functions, digestion, 

 absorption, circulation, respiration, the secretions and digestion are per- 

 formed as in man, and in that respect there exist between them very 

 slight differences; nay, in some animals, these functions are performed 

 with much more energy. Thus several animals digest substances, on 

 which our own organs produce no effect, and others (birds) have a more 

 rapid circulation, a more active nutrition, and evolve more heat. But not 

 one of them is as well provided with organs to keep up intercourse, as a 

 living being, with the surrounding objects. In no one animal, are the 

 senses possessed of the same degree of perfection ; the eagle, whose sight 

 is so piercing, has a very dull sense of touch, taste, and smell. The dog, 

 whose smell is exquisite, has a very ordinary extent of sight: in him, the 

 the taste and touch are equally imperfect. His touch, in the perfection 

 of which no animal comes up to man, has not been improved in delicacy 

 at the expense of the other senses. The sight, the hearing, the taste, 



