23 ANIMAL MECHANISM. 



mechanism by which the blood circulates in the vessels, how 

 air penetrates into the lungs, and escapes from them alter- 

 nately, how the intestines and the glands are perpetually 

 affected by slow and prolonged contractions. All these move- 

 ments take place within the organs without the exercise of the 

 will ; frequently even the individual in whom they occur is 

 unconscious of them ; these are the acts of organic life. 



Other movements are subjected to our will, which regulates 

 their speed, energy, and duration; these are the muscular 

 actions of locomotion, and the different acts of the life of rela- 

 tion. We shall treat specially of this order of phenomena, 

 which are more easy to observe, and to analyse. Suffice it 

 here to say that the absolute division between the acts of 

 organic life and those of the life of relation ought not to be 

 accepted unreservedly. Bichat, who established it, based it 

 upon anatomical and functional differences which are of less 

 importance now than they were in his time. The mus- 

 cular element of organic life is unstriped fibre obedient to the 

 nerves of a particular system called the great sympathetic, 

 on which the will has no action ; motions produced by this 

 kind of fibre are manifested some time after the excitement of 

 the nerve or of the muscle, and continue for a considerable 

 time. In fact, the object of those acts which are intended to 

 maintain the life of the individual imprints upon them a 

 special character. The muscular element of the life of rela- 

 tion consists of a fibre of striated appearance, whose action, 

 under the control of the will, is dependent upon nerves 

 emanating directly from the brain or from the spinal marrow. 

 These movements become evident rapidly as soon as they are 

 provoked by excitement; they are of brief duration, and are, 

 generally, not indispensable to the maintenance of the life of 

 the animal. 



Although this distinction is, in a general way exact, it is 

 plain that it is too arbitrary, and that numerous except ions 

 to the anatomical and physiological laws which it tends to 

 establish may be quoted. Thus, the heart, an organ directly 

 indispensable to organic life, and not under the governance of 

 the will, is a structure which much resembles the voluntary 

 muscles. Certain fishes of the genus tinea have striated muscles 



