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on my mind, is, that perhaps the ultimate arrangement of matter, like its ultimate particles, may form a subject too subtile for human perception.., Our information in these respects must be limited, as our powers of perception have their bounds. The imperfection of the human senses does not, however, seem a subject of regret; because it induces ą greater necessity for the exertions of intellect; and many subjects appear far more demonstrable to reason than to sense.
Fontana, it must be granted, possessed considerable talent in microscopical observations, for he says, that he could readily distinguish the nature of
animal substance, which might be placed on the field of his microscope, by regarding its ultimate fibres, and according to , him the muscular fibres . are much smaller than those of the nerves. Proscaska and others
assert, that the ultimate muscular fibres are continued throughout the whole length of a muscle. How marvellous, (could we but see it,) would such a slender thread appear, continued throughout the whole length of the human sartorius. Haller) however, affirms, that the fibres are not continued, but that one. set: terminating another begins. Suspecting that Haller employed the solar microscope on this occasion, as he says he had done on others, I examined muscular fibres with this instrument. Now though I place no confidence in my own observation, and think the subject unimportant as to any conclusion that may be deduced from it, yet I will tell you how au portion of a muscle appeared to me when magnified about 500 times. The fibres were slightly, undulating, and one seti terminating, another began: neither were the sets of fibres of considerable length. The mus
cular fibres were connected by cross threads of common cellular substance.
Mr. Carlisle, in whose talents and accuracy we are all disposed to place confidence, in the Croonian Lecture, printed in the Philosophical Transactions for 1805, says, that he can distinctly see an ultimate muscular fibre, which he describes « as a solid cylinder, the covering of which is reticular membrane, and the contained part a pulpy substance irregularly granulated.”
He has also described the termination of nerves in muscles. Muscles are liberally supplied both with blood vessels and nerves, but nothing peculiar is perceived in their distribution. 'We make them very red by injecting them, and we see numerous nerves entering their substance
at various places. Yet the vessels of some muscles are too minute to receive red blood or our coloured injections, so that redness though a common is not an essential character of muscle:
I here willingly relinquish the enquiry into the structure of those organs in which the irritable property chiefly resides, in order, in the next place, to speak of the principal phænomena of irritability.
Muscles have the power of contracting with surprizing celerity and force. It seems indeed wonderful that the biceps muscle of the arm, which in the dead state would be torn by the weight of a fèw ounces appended to it, shall in the living state be capable of lifting and sustaining more than 100 lbs. The matter in the muscle seems neither to be in
creased nor diminished during its contraction, what is lost in length being gained in bulk. The voluntary contraction of muscles cannot be long continued; they become weary, and painful, the contraction remits and recurs, causing a tremulous motion. Yet this phænomenon does not seem to be the effeet of absolute inability, in the irritable : property, to continue in action, for some muscles continue to act without experiencing fatigue. For instance, those of the jaws and back; for whenever they relax, the jaw drops, and the head and body fall forwards, las. we see in persons who are going to sleep in a sitting posture. . Certain sphincter muscles likewise remain in action without experiencing fatigue. Some sphinc: ters also, I may add, are disposed to yield considerably without impatience; so that their irritability resembles that of those muscles which Bichật has considered as