Viewing page 286 of 504
This transcription has been completed. Contact us with corrections.
[start page] 95 But if this effect is constantly produced soon after death, how much more when the animal is alive? Therefore a muscle of voluntary motion, in its natural state, in a living animal body, will contract, by the introduction of a warm mild fluid, into its fleshy substance, in every part: Which was to be proved. [[left margin]] Objection. [[left margin]] But here it may be objected, with some appearance of reason, that there is a warm fluid, the living blood, in every part of the fleshy substance of all the muscles, during the life of the animals; and yet it is a fact, that no muscle of voluntary motion contracts, but at the command of the will, morbid cases excepted. This objection comes close to the original question, and however reasonable it may seem, will quickly vanish before some common observations concerning the objects of sense in general, and this manner of operation upon the different organs, so far as it universally agrees. [[left margin]] Nerves, the immediate instruments of sensation, (V.p. 108) Which is merely relative. [[/left margin]] We must first beg leave to make an easy postulatum, [[underlined]] viz. [[/underlined]] that the nerves are the immediate instruments of sensation, though they are differently organized for the different senses. [[underlined]] Observations, proving that the sensations of which we take cognizance are merely relative. [[/underlined]] It is a certain fact, that, in the several senses, the proper objects being supposed present, the sensation is entirely relative; or, in other words, that the presence of a powerful object always obliterates the present sensation of a weak object; and that the constant habitual presence of any one object, in the same given degree, produces no sensation at all. [[left margin]] Instances. [[/left margin]] Thus we observe, that the light of the sun extinguishes the light of the stars; a stronger [[strikethrough]] taste[[/strikethrough]] taste covers a weaker; the sound of a drum drowns an ordinary human voice; itching is banished by smart and pain; a weak scent, by one that is strong; cold, or a less degree of warmth, by heat, or a greater degree of warmth; and universally, our daily experience demonstrates to us, that every organ of sense, made familiar to a given degree of its object, affords no manner of sensation of the object in the given degree. Thus it fares with the warm blood, which has constantly flowed through the whole minute substance of every muscle of voluntary motion in an animal body, from the time of their formation, or unfolding in the womb. And it is highly probable, that the quickening of the child in a woman is no other than the completion of that state, in which the blood begins freely to flow through, and to affect the instruments of voluntary motion; and till it becomes familiar to them, produces those frequent shudders, or general muscular contractions in the whole frame of the foetus, which for a fortnight or more are the constant signs, that is has now obtained an animal life. And here arises an apparent difference, though it will be found the greatest uniformity, between the muscles of voluntary and those of involuntary motion; and namely the heart; which being appointed to protrude the vital fluids during the life of an animal, has a short alternate remission of its contracting cause; and is thereby render'd capable of admitting a constant and necessary supply of labour and stimulus together, without any force, or contraction, to the natural order of the whole. [[right corner]] [[?]] [end page]
