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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 a 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 muscular fibres were connected by cross threads of common cellular substance. y

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 phaenomena 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 few 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 increased 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 phaenomenon does not seem to be the effect of absolute inability, in the irritable to 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, as we see in persons who are going to sleep in a sitting posture. Certain sphincter muscles likewise remain in action without experiencing fatigue. Some sphincters also, I may add, are disposed to yield considerably without impatience; so that their irritability resembles that, of those muscles which Bichât has considered as a distinct class, and subservient alone to what he calls the organic life. The contractile power of muscles is also capable of remaining in vehement action for a great length of time, as we see in some cases of cramps, and still more in some cases of tonic tetanus, ... . . . . ; - * * * * Yet though the irritable power is not incapable of continued exertion, it seems evidently to be in general susceptible of fatigue, and inclines to be at rest. If we stimulate the muscles of a limb of a frog severed from the body, by voltaic electricity, the muscular actions are at first vivid and forcible, but they grow fainter and feebler on repeated excitement, Yet if we wait a little till they seem to regain their power, they become vivid and forcible as at first from the same degree of excitement. Such actions may be

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