152 ANIMAL-SENTIENT FORCES. [i. 



mencement^ but it is regulated by sensational and intellectual 

 volitions, according to the requirements of other instincts, 

 emotions, intellectual desires, &c., into laughing, or weeping, 

 or sighing, speaking, &c. It is incontrovertible, that these, 

 together with groaning, sobbing, cooing, moaning, screaming, 

 coughing, whistling, sneezing, and all other changes of the 

 respiratory movements which are caused by external sensations 

 or obscure complex conceptions, are in so far true sentient 

 actions of satisfied instincts, since the respiratory actions gene- 

 rally belong to this class. 



286. It is manifest from the considerations already advanced, 

 that there are two classes of instincts ; the one comprising 

 those in which the acts are under the control of the animal, 

 so that they can be induced or intermitted at will (283^ — 285) ; 

 the other, comprising those in which the acts are the purely 

 corporeal functions of the mechanical machines, as in hunger 

 and thirst (281, 282). There are some instincts of both classes, 

 however, which gradually change into one or the other class. 

 Thus, at first, in children and animals the unpleasant external 

 sensations resulting from accumulation in the bladder and 

 rectum, and which bring the appropriate instinct into opera- 

 tion, are relieved in a natural and necessary manner, because 

 the sphincter muscles are compelled by mere physical pressure 

 to permit the exit of accumulated excretions ; afterwards, how- 

 ever, this takes place when the unpleasant external sensation 

 is again felt, by a voluntary relaxation of the sphincters. In 

 the same way, the first respiratory movement in a newly-born 

 animal is probably the natural and necessary result of a very 

 obscure external sensation ; but, afterwards, it takes place by 

 a voluntary movement of the thorax on the recurrence of the 

 unpleasant sensation (285). And, on the contrary, we seek 

 at first to avoid many pains and other unpleasant external sensa- 

 tions by voluntary movements, which afterwards become purely 

 automatic, as, for example, shouting, writhing, and retracting 

 when in pain; the quickened walk and the drawing up of the legs 

 to the body in severe cold ; the contraction of the eyelids in a 

 strong light; and a thousand other movements, the objects of 

 instincts, formerly volitional, but become mechanical from 

 frequent repetition. Neither can we infer that the sentient 

 actions of an instinct which, in us or in another animal, are 



