the clamp on the left. In order to use this hammer for the production of inductive currents, the one coil, A, of the apparatus (shown in fig. 10, p. 31), must be inserted. between the two clamps shown on the right.1

Wagner's hammer in a more simple form may be permanently connected with coil A. In this case it is best to place the second coil B on a sliding-piece which is so arranged that it can be moved along a groove to a

greater or less distance from coil A. This enables the operator to regulate the strength of the inductive current generated in it. Fig. 13 represents an apparatus of this sort. The secondary coil, in which the inductive currents originate, is in this case indicated by i; the primary coil, through which the constant currents pass, by c; b is the electro-magnet; h the armature of the hammer; f is a small screw, at the point of contact of which with the

In order to set Wagner's hammer itself in motion, these clamps must be connected by a wire through which alone the connection from the point to the coils of the electro-magnet is made.

small plate soldered on to the surface of the German silver spring the current is closed and interrupted. An apparatus of this kind is called a sliding inductorium. It is only necessary to attach the ends of the coil i to the muscle, and to insert the chain between the columns a and g. The action of the hammer then at once

commences; the inductive currents generated in c pass through the muscle, which contracts tetanically.

Instead of connecting coil c immediately with the muscle, it is better to carry the wires from the coil to the two clamps b and c in the apparatus shown in fig. 14, which is called a tetanising key. Two other wires pass from these same clamps b and c to the muscle. When the inductive apparatus is in action the muscle is put into a tetanic condition. But as soon as the lever d is pressed down, so as to connect b and c together, the current of coil i is

FIG. 14. TETANISING KEY OF enabled to pass through this lever. The lever d being made of a short and thick piece of brass, which offers hardly any resistance to the current, while the muscle on the contrary offers great resistance, very little of the current passes through the muscle, but nearly all through the lever d. The muscle, therefore, remains at rest. As soon, however, as the lever d is again raised, the inductive currents must again pass through the muscle.

A slight pressure on the handle of the lever d is, therefore, sufficient to produce or to put an end to the tetanic condition at the will of the operator, thus allowing more accurate study of the muscle processes.

We have now noticed muscle in two conditions: in the ordinary condition in which it usually occurs either within the body or when taken from the body, and in the contracted condition which results from the application of certain irritants. The former condition may be spoken of as the rest of the muscle, the latter as the action of the muscle. Muscular action occurs in two forms, one of which is a sudden temporary shortening or pulsation, while the other is an enduring contraction or tetanus. The latter, on account of its longer duration, is more easily studied. In many cases it is a matter of indifference whether pulsating or tetanised muscle is examined. In the following investigations we shall therefore employ sometimes one, sometimes the other, method of irritation.

3. On attaching weights to a muscle, the latter is capable of raising these weights so soon as it is set in motion. It raises the weight to a certain height, and thus accomplishes labour which, in accordance with mechanical principles, can be expressed in figures by multiplying together the weight raised and the height to which it is raised. This height to which the weight can be raised, which may be called the height of elevation of the muscle, can be measured by means of the myograph already described. On attaching a weight to the lever of the myograph, the muscle is immediately extended. The pencil must now be brought in contact with the glass plate of the myograph, and the muscle must be made to contract by opening the

key so as to allow the inductive currents to have access to the muscle. The latter at once shortens, and its height of elevation is indicated by a vertical stroke on the smoked glass plate. On instituting a series of experiments with the same muscle but with various weights, it will be found that the muscle is not able to raise all weights to the same height. When the weight is small the height to which it is raised is great. As a rule, as the weight increases, the height to which it is raised becomes less, and finally, when a certain weight is reached, it becomes unnoticeable. Fig. 15

FIG. 15. HEIGHT OF ELEVATION CONSEQUENT ON THE APPLICATION OF VARYING WEIGHTS.

shows the result of a series of experiments of this sort. The figures under each of the vertical strokes represent in grammes the amount of the weight raised; the height of the strokes is double the real height of elevation, the apparatus employed in the experiment representing them twice their natural size. Between each two of the experiments the glass plate was pushed on a little further in order that the separate experiments might be indicated side by side. In finding the first of these heights of elevation, under which stands an 0, no weight was applied, and even the weight of the indicating lever was neutralised by an equivalent weight. It appears, therefore, that the height of elevation is

greatest in this case. Each of the succeeding heights begins from a somewhat lower point in consequence of the extension of the muscle by the applied weights. But each also rises to a less height than that which preceded it; and, finally, a weight of 250 grammes being applied, the height of elevation is naught.

From this series of experiments it is evident that, as the weight increases, the height to which it is raised. continually decreases. The following conclusion must, therefore, be drawn as to the work accomplished by the muscle. When no weight is applied, the height of elevation is great; but as no weight is raised in this case, the amount of work accomplished, therefore, also equals 0. When 250 grammes, the greatest weight, is applied, the height of elevation equals 0, so that in this case also no work is accomplished. It was only on the application of the intermediate weights that the muscle accomplished work; and this, moreover, at first increased until a weight of 150 grammes was reached, and then gradually decreased. On calculating the amount of work accomplished during each of the pulsations in question, the following results are found :—

The same results may be obtained with any other muscle. So that it may be stated as a very general proposition, that for each muscle there is a definite weight, on the application of which the greatest amount of work is accomplished by that muscle; when greater or less weight is applied, the amount of work accomplished is less. But the height of elevation corresponding with the application of one and the same weight is