This brings us back again to muscle, for the object of nearly all the voluntary muscle is to cause movement among the bones. For this purpose the muscle cells or fibres are arranged parallel to one another, and bound up together by connective tissue, the whole bundle being known as ‘a muscle.’ The two ends of a muscle are attached to two bones by connective tissue, which sometimes forms a short cord, or tendon. Then, when the muscle contracts, the two places of its attachment are pulled towards one another, and something has to move. But before saying more about the way in which the bones are jointed and muscles attached—in fact, what movements are possible in the human body—it would be as well here to describe the chief properties of muscle and the way in which they are studied.
II.
Diagram 21.—Apparatus for recording a Muscular Contraction.
The way in which voluntary muscle is studied is very simple. A frog is killed by thrusting a probe into the brain and down the spinal cord, and a muscle is then dissected out and attached to a piece of apparatus ([see Diagram 21]) in such a way that on its contracting it raises a lever, and draws a line on a moving surface. The rate at which the surface is moving is ascertained, so that the nature of the curve, which is a graphic record of the contraction, can be analyzed. ([See Diagram 22.]) For instance, when an electric shock is used to make the muscle contract, we find that a slight shock causes a small contraction, as shown by a low curve, while a stronger one, up to a certain point, causes an increase.
Diagram 22.—Graphic Record of a Response to a Single Stimulus applied at A.
Lower line = tuning-fork records of ⅟₁₀₀″.
But having described how muscle is studied, it is only necessary to state a few facts concerning it; to discuss muscle, fully describing the experiments by which its more obscure properties have been elucidated, and the devices by which causes of error have been eliminated, would fill volumes.
