OBSERVATIONS ON IRRITABILITY. 191 any figns of life remain in the bodies of animals, or in any of their parts, this principle ftill continues to aCluate them. There are two kinds of motion from irritation obfervable in living animals, viz, where the mufcle or organ itfelf is flimulated ; and where the fiimulus only affe&s fome neighbouring or diflant part. The fir it (of which kind is the motion of the heart) feems to be owing to the foul or fendent principle as acting in the part moved ; but the fécond, to the foul as perceiving and a ding in the brain : and of this kind is the motion of fneezing from an ir¬ ritation of the nofe, and the contraction o.f the diaphragm in vo¬ miting and in a tenefmus or flrangury. In order to the firft kind of motions, an immediate communication with the brain is not abfolutely neceffary, but only fuch a fhare of the nervous power in the mufcle or its nerves, as may be requifite to fit its fibres for be¬ ing aCled upon by the foul or fendent principle. But the cafe is quite otherwife in the fécond ; where the motion produced is thro’ the intervention of the brain, and not by any ßimulus applied to the part moved. And hence it is, that, in an animal newly dead, the diaphragm is not brought into contraction by lacerating or pricking the inteßinum return or neck of the bladder, although the fibres of thefe parts themfelves may be thereby agitated with fome tremulous motions. In like manner, though the mufcular coat of the ftomach is excited into contraction fome time after the death of an animal by irritating it ; yet the diaphragm is not afîëCted by this irritation : which, however, it would have been, if the animal had been alive. Agreeably to this, when any of the mufcles of the legs of a frog are irritated fome time after cutting off its head, almofl all the mufcles belonging to the legs and thighs are brought into contraction, if the fpinal marrow be entire : but, as foon as it is deftroyed, although the fibres of fuch mufcles as are them¬ felves flimulated are affeCted with a weak tremulous motion, yet the neighbouring mufcles remain at perfeCt refh I have elfe where endeavoured to fhew, that the fuppofition of the foul or fentient principle’s continuing for fome time to aCtuate O o a the