. A text-book of animal physiology, with introductory chapters on general biology and a full treatment of reproduction ... Physiology, Comparative. THE CONTRACTILE TISSUES. 169 in general. It is important to beai* in mind that ciliary action may go on in the cells of a tissue completely isolated from the animal to which it belongs, and though influenced, as just ex- plained, by the surroundings, that the movement is essentially automatic, that is, independent of any special stimulus, in which respect it differs a good deal from voluntary muscle, which usually, if not always, contracts only whe
. A text-book of animal physiology, with introductory chapters on general biology and a full treatment of reproduction ... Physiology, Comparative. THE CONTRACTILE TISSUES. 169 in general. It is important to beai* in mind that ciliary action may go on in the cells of a tissue completely isolated from the animal to which it belongs, and though influenced, as just ex- plained, by the surroundings, that the movement is essentially automatic, that is, independent of any special stimulus, in which respect it differs a good deal from voluntary muscle, which usually, if not always, contracts only when stimulated. The lines along which the evolution of the contractile tissues has proceeded from the indefinite outflowings and withdraw- als of the substance of Amoeba up to the highly specialized movements of a striped muscle-cell are not all clearly marked out; but even the few facts mentioned above suffice to show gradation, intermediate forms. A similar law is involved in the muscular contractility manifested by cells with other func- tions. The automatic (self-originated, independent largely of a stimulus) rhythm suggestive of ciliary movement, more manifest in the earlier developed smooth muscle than in the voluntary striped muscle of higher vertebrates, indicating further by the regularity with which certain organs act in which this smooth muscular tissue is predominant, a relation- ship to ciliary movement something in common as to origin—in a word, an evo- lution. And if this be borne in mind, we believe many facts will appear in a new light, and be invested with a breadth of meaning they would not otherwise possess. The Irritability of Muscle and Nerve.—An animal, as a frog, deprived of its brain, will remain motion- less till its tissues have died, unless the animal be in some way stimula,ted. If a muscle be isolated from the body with the nerve to which it belongs, it will also remain passive; but, if an electric current be passed into it, if it be pricked, pinc
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