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muscles is fatigued, or when it is feeble, their vibratory or tremulous motions are manifest to common observation, but the same kind of motion may be perceived at all times by attention, as has been shewn by Doctor Woolaston in the Croonian Lecture for the year 1810. It is then I think manifest, that Mr. Hunter's conjectures are the most probable of any that have been offered as to the cause of
My allotted time does not permit me at present to consider the other vital functions; yet I relinquish the subject with reluctance, because I have been speaking only on that point in which it seems most difficult to persuade the incredulous, of the probability and rationality of Mr. Hunter's Theory.
When hereafter I shall have to speak
of the other vital functions, I think it will appear that it is impossible to account for the phaenomena in any other manner than that which Mr. Hunter has suggested.
In ascending the difficult and lofty ladder of knowledge, men of great talent and industry seem to have affixed to it certain resting places, on which, reposing for a time from their labours, they could tranquilly assemble their followers, and contemplate more extensive views of nature, and of nature's laws, than had before been taken. If after having stood by the side of the great teacher Newton, and learned from him the properties of common and inanimate matter, we afterwards attend to Mr. Hunter, our great instructor in the functions of living beings, he points out to us how matter, starting from the general mass, springs up into life in ve. getation. We see vegetables as it were self formed and producing their own species. We observe them also exerting most of the powers which animals possess. That they have irritability is evident from the current of their sap and their secretions; nay, in some we observe those vivacious motions which seem chiefly to belong to animal life, as is evident in the Mimosa, the Dionea Muscipula, and Heydysarum gyrans. We see them like animals having alternate seasons of action and repose; and though in general vegetables like animals are in action during the day and rest in the night, yet also some vegetables like some animals rest in the day and are in action during the common season of repose.
We see animals scarcely differing from vegetables in their functions, like them doomed to a stationary existence, with
even less appearance of organization than we usually discover in vegetables, and of a structure so simple as to admit of propagation like vegetables by cuttings. Yet in all the diversity of living beings we recognize certain processes peculiar and essential to life; as the power of converting other kinds of matter into that appropriate to the individual it is to form and support; the power of distributing the nutriment, thus converted, to every part for its formation and supply; the ventilation, as I may call it, of the nutritive fluids; the power of preparing various dissimilar substances from the nutritive fluids; and the propagation of the species. As what is deemed the complexity of animal life increases, we find distinct organs allotted for each of these functions; thus we have organs of digestion, circulation, respiration,
secretion, and generation, which are va. rious in their structure in the different tribes of animals,
In vegetables, and in some moluscae, no traces of nerves are discoverable. The nervous system begins in a simple form, and seems to increase in complexity up to man. But this will make the subject of the next lecture. Mr. Hunter also shews us that there are animals, as for instance the torpedo and gymnotus, which have organs liberally supplied with nerves, forming an electric battery which they can charge at will. Such facts shew to what a degree electricity exists in these animals, and how greatly it is under the influence or control of the nervous system; and they could not fail to make a strong impression on the contemplative and deeply meditating mind of Mr. Hunter.