7 i8 



TEXT-BOOK OF PHYSIOLOGY. 



Six double binding posts for the attachment of wires pass through the 

 platform. Near the side of the upper surface of the platform there rises a 

 vertical rod, carrying a clamp for holding the femur of a nerve-muscle prep- 

 aration, as well as a horizontal rod for supporting at least three pairs of 

 non-polarizable electrodes. A groove around the outer edge of the platform 

 receives a glass shade, which covers the whole. The air of the chamber is 

 kept moist by placing in it pieces of blotting-paper saturated with water. 



From the under surface of the platform there descends a rod, which, by 

 means of a double binding screw, supports a horizontal rod, modified at one 

 end to carry the delicate axis of a light stiff recording lever. The end of this 

 lever is pointed, to enable it to write on a smoked glass or paper. Beneath 

 the axis is a strip of brass, carrying a screw, which gives support to the lever 



FIG. 369. MOIST CHAMBER. 



until the instant the contraction of the muscle begins. This screw, the 

 after-loading screw, also enables the lever to be placed in a horizontal position. 

 The portion of the lever near the axis is provided with a double hook, the 

 lower portion of which serves for the attachment of the weight by which the 

 muscle is counterpoised. 



In some experiments, as in the registration of a muscle contraction under 

 varying conditions, it is necessary to give the lever mass by attaching weights 

 directly beneath the muscle. This, however, introduces certain errors in 

 the movements of the lever, which somewhat deform what would otherwise 

 be the normal curve. If the weight be attached, not opposite to the muscle 

 attachment, but close to the axis of the lever, the undesirable acceleration 

 of the lever movement, during both contraction and relaxation, is largely 

 prevented. The lever may be a straw, a strip of celluloid or aluminium. 

 It should be as light as possible. The writing point may be made of stiff 

 paper, a piece of tinsel, glass, or aluminium. It should have sufficient elas- 



