MECHANICAL RESPONSE OF NERVE 527 



that, as the record is made by the moving spot of light, the 

 recording-point, as it were, encounters no friction, and the 

 characteristic form of the response curve is thus unmodified. 

 But prolonged work in the photographic dark-room is very 

 fatiguing to the observer. I was, therefore, desirous of so 

 perfecting the ordinary mode of record by the movement of 

 the tracing-point of a lever over a smoked surface, that it 

 would be adequate for most purposes. The difficulties 

 involved in carrying this out lie, first, in the obtaining of a 

 sufficiently high magnification, and, second, in the overcoming 

 of friction at the writing point. A long lever, such as is 

 necessary for high magnification, entails a heavy weight. 

 But this can be obviated by employing a light and thin 

 aluminium wire, 50 cm. in length. The fulcrum-rod, to 

 which the lever-index is attached, has a diameter of 2 mm. 

 A thread attached to the contracting nerve is wound once 

 round this fulcrum-rod. The radius of the latter being I mm., 

 the magnification produced by this arrangement is 500 

 times. The magnification may in this manner be raised as 

 high as 1,000, by taking a longer lever. For the tracing 

 point the end of the lever is bent at right angles, and a fine 

 bristle attached. Even this degree of magnification is not 

 always necessary, as I have already said. The records which 

 immediately follow have a magnification of only fifty times. 



The next difficulty, as already stated, lies in the friction 

 to be overcome. The friction offered by a writing-surface of 

 smoked paper is too great to be employed. A surface of 

 plate-glass, coated with a thin and uniform layer of smoke, 

 offers considerably less resistance. But even this retards the 

 free movement of the tracing-point. I was therefore led to 

 the construction of my Oscillating Recorder. The glass 

 plate, on which the record is made, is carried on a primary 

 frame, which is moved at a uniform rate, regulated by clock- 

 work, on wheels, over rails. The plate is mounted on this 

 primary frame in a secondary frame, which is held away from 

 the primary, at a certain fixed distance, by means of spiral 

 springs. This secondary frame, by means of an electro- 



