change in length of the muscle, but of its change in thickness, by enclosing it in a kind of pincers, one of the movable branches of which (myographical pincers, Marey) operates on a registering apparatus. Of course, we find the same simple shocks, or elementary contractions, and the same fusion of these shocks in physiological tetanus, as with the former method, but the process is more practical, and may be made use of, for instance, to register the contractions of the biceps in man.

III. SMOOTH MUSCLES.

THE smooth muscular fibres (Fig. 21) are situated chiefly in the coats of the viscera (intestine, bladder, uterus, etc.), or in the tubes which open into or proceed from them

(the bronchus, ureters, urethra, bile duct, etc.). It is thus difficult to form a distinct group of this contractile element, for the purpose of making it a special study.

Still, by studying the smooth muscles as we find them with all the normal intricacies of their fibres, we are easily convinced that these elements, like the striated fibre, possess the property of appearing under two different forms, which we may still call first and

second.

The smooth muscle appears to possess, under these two forms, the same properties as the striated muscle under similar forms, as well in regard to its chemical reactions, as to

scope, the reader is referred to a monograph by Professor Thomas Dwight, Jr. (Boston Nat. Hist. Soc. Proceedings, Nov. 5, 1873.)

*A, A fasciculus, from which proceed, in a, a, detached cell fibres. b, Represents it in section. B, A similar fasciculus, having been exposed to the action of acetic acid: the nuclei appear long and slender. a and b, as above. 300 diain. (Virchow, Pathologie Cellulaire.)

the electro-motor force, elasticity, and respiratory exchanges (combustion). But what distinguishes the smooth muscle from the striated muscle is that in the former the passage from the first to the second form is made with extreme slowness. After the excitation which irritates the fibre, and gives rise to its change of form, a considerable time always elapses before the change occurs. As this latent excitation lasts a long time, so the contraction which follows is produced very slowly, continues for some time at its height, and then gradually relaxes.

Thus, the only consequence of the difference in structure of the smooth muscles is that they yield less readily to the influence of irritants, and contract more slowly than the other muscles. They also pass into the state of cadaveric rigidity in the same manner as the striated muscles. A state of transition between the striated muscles and the smooth muscles, properly so called, is also sometimes observed. This is the case, up to a certain point, with the muscular tissue of the heart. (See p. 86.)

On resuming a series of investigations as to the comparative physiology of the smooth and the striated muscles, M. Legros and M. Onimus arrived at the following conclusions: in the case of the striated muscles both the contraction and the return to a state of repose are rapid, while in that of the smooth muscles both are slow. These movements are always involuntary. The contraction (physiological tetanus) of the former is caused by a series of shocks, while that of the latter comes on gradually, without oscillation. The peristaltic form (see intestine) is that in which these contractions most frequently appear. The motility (excitability) lasts longest in the smooth muscles after death. In the striated muscles electrical excitation of the motor nerves of the muscle produces more effect than that of the muscle itself; with the smooth element the reverse is the case. Finally, if the two poles of an induced current be made to act upon the smooth muscles, by placing these poles at a certain distance from each other, we find, in the intestinal tube, for instance, that instead of the whole muscle contracting, those parts only contract which come in contact with the poles; in the intermediate parts there is no contraction, but rather relaxation. The effect produced by continuous currents is still more remarkable: in those organs which have peristaltic movements (see intestine, vaso-motors) there are variations corresponding with the direction of the current; when this

follows the direction of the normal peristaltic contractions, relaxation takes place, while if it goes in a contrary direction, contraction is produced.

IV. CONTRACTILE CELLS.

THE different properties of the contractile cells resemble closely those which we have studied in the cells in general, especially the faculty which they possess of changing their form. This property being common to the whole mass of protoplasm, we will here, after speaking of the muscle properly so-called, mention only those contractile cells which are of special use in the system, on account of their contractility or irritability. Now these elements are to be found scarcely anywhere fully developed, except in the arteries, in the smaller arteries especially. Thus, in order to study the functions of these embryonic muscular forms, we must examine the small vessels. (See circulation.)

We

Among the movements which take place in the cells, we must also mention the movements of the vibratile cells. shall speak of these in reference to the cylindrical epitheliums which are found to have this ciliary covering.

V. ADJUNCTS OF THE MUSCULAR SYSTEM.

(Connective Tissue, Bones, Tendons.)

General Mechanism of the Muscles.-The muscular fibre, in changing its form, plays an important part in the system as the source of labor and of movement. For this purpose it is in close relation with other organs, and exhibits two different tendencies, acting either by compression or by traction.

In the former case (pressure) the muscular elements are arranged in the form of handles or rings, or even of membranous pouches, in such a manner as to compress on all sides the organs which they enclose. The sphincters, the muscular tubes (pharynx, œsophagus), and the heart, as well as all the hollow contractile organs, are formed according to this plan. Nearly all the muscles of the organic life (smooth muscles) exhibit this arrangement. Their function is, generally, to further the passage of the liquid, or, at all events, softened matters, into the interior of the reservoirs and tubes of which they form the walls, and they attain their end by

means of the unequal pressure which they produce in these reservoirs, liquids having always a tendency to move towards the point of least pressure. (See movements of the stomach, of the intestine, the bladder, uterus, etc.)

In the latter case the muscular fibre is inserted in the organs which it is intended to affect, in the levers which it is to move (bones) by the medium of resisting cords (tendons). The study of the ligaments belongs to that of the bones (and of their articulations); the study of the aponeuroses, to that of the tendons and the muscles. The bones,

Fig. 22-Section of diaphysis of cartilage.*

the articular cartilages, the ligaments, the tendons, the aponeuroses, thus constitute the passive organs of locomotion. The tissues of these organs are so associated in histological and chemical peculiarities, that they have been classed together, and form a vast family, called group of connective or collagenous tissue. The tendons, the aponeuroses, the ligaments, and the connective substance of the organs form the connective or cellular tissue, properly so called.

Connective Tissue, properly so-called. This tissue has

c, c, Calcified cartilage. c', o, The calcareous salts are just beginning to be deposited. p, Perichondrium. 350 diam. (Virchow, "Pathologie Cellulaire.")

the closest connection with the muscular element, and it is this which, under the names of perimysium and enveloping aponeurosis, unites the muscular fibres in clusters or masses of flesh, so as to admit of united action on the part of the contractile elements; but this tissue is found to be distributed, not only in the muscles, but throughout the other organs: it was formerly called cellular tissue, but this name is inadequate, for it expresses only a general disposition of the tissue, by means of which it is easily penetrated by the gases or liquids which it encloses in vacuoles or cells (in the macrographic sense of the word). The whole body may be looked upon as a mass of connective tissue, or of one of its different forms, in which the more essentially active elements are located. Thus, this tissue has a large share in the composition of the nervous centres, prevailing even over the nervous tissue, properly so-called; and the knowledge of this

fact has lately given rise to entirely new views as to the nature of diseases of the cerebro-spinal centres, and even of the nerves in general; as, for instance, in sciatic neuralgia, in which the pathological change is generally produced in the cellular tissue of the sciatic nerve.

The connective tissues are generally rich in embryonic or plasmatic globules (see above, p. 21), or their derivatives: cartilaginous cell, bony cell (Figs. 24 and 25). In some places these globular elements appear to have a certain

*The cornea is here cut parallel to its surface. The star-shaped corpuscles (embryonic globules or plasmatic cells) are seen flattened out, together with their anastomotic prolongations (His).