22 INTRODUCTION. 



tne knowledge of the mk, so that the will is inaeed one means of causing the fibres 

 to act, but which is neither general nor exclusive. 



The fleshy fibre has for its base a particular substance termed fihrine, which is 

 insoluble in boiling water, and of which the nature appears to be to take of Itself this 

 filamentous form. 



The iwtritive fluid, or the hhod, such as we find in the vessels of the circulation, not 

 only resolves itself principally into the general elements of the animal body, — carbon, 

 hydrogen, oxygen, and azote, but it also contains fibrine and gelatine, all but disposed 

 to contract, and to assume the forms of membranes or of filaments peculiar to them ; 

 nought being ever acquired for their manifestation but a little repose. The blood pre- 

 sents also another combination, which occurs in many animal solids and fluids, namely, 

 albumen [or ivhite of eg(/~\, the characteristic property of wdiich is to coagulate in 

 boiling water. Besides these, the blood contains almost all the elements which may 

 enter into the composition of the body of eacli animal, such as the lime and phosphorus, 

 which hardens the bones of vertebrated animals, the iron, which colours the blood itself 

 as well as various other parts, the fat or animal oil, which is deposited in tlie cellular 

 substance to maintain it. &c. All the fluids and solids of the animal body are composed 

 of chemical elements contained in the blood ; and it is only by possessing some ele- 

 ments more or less, or in different proportions, that each is severally distinguished ; 

 whence it becomes apparent that their formation entirely depends on the subtraction 

 of the whole or part of one or more elements of the blood, and, in some few cases, on 

 the addition of some element from elsewhere. 



The various operations, by which the blood supplies nourishment to the solid or liquid 

 matter of all parts of the body, may take the general name of secretion. This terra, 

 however, is often exclusively appropriated to the production of liquids, ■^'idiile that of 

 nutrition is applied more especially to the production and deposition of the matter 

 necessary to the growth and conservation of the solids. 



Every solid organ, as well as fluid, has the composition most approjiriate for the ofiice 

 which it has to perform, and it preserves it so long as health continues, because the 

 blood renews it as fast as it becomes changed. The blood itself, by this continual 

 contribution, is altered every moment ; but is restored by digestion, which renews its 

 matter ; by respiration, which sets free the superfluous carbon and hydrogen ; and by 

 perspiration and various other excretions, that relieve it from other superabundant 

 principles. 



These perpetual changes of chemical composition constitute part of the vital vortex, 

 not less essential than the visible movements and those of translation : the object, in- 

 deed, of these latter is simply to produce the former. 



OF THE FORCES WniCH ACT IN THE ANIMAL BODY. 



The muscular fibre is not only the organ of voluntary motion ; we have seen that it 

 is also the most powerful of the means employed by nature to efi"ect the move- 

 ments of translation necessary to vegetative life. Thus the fibres of the intestines pro- 

 duce the peristaltic motion, which causes the aliment to pass onward along this canal ; 

 the fibres of the heart and arteries are the agents of the circulation, and, through it, of 

 all the secretions, &c. 



