32 THE PHILOSOPHY OF BIOLOGY 



The figure represents a tracing made by a muscle- 

 nerve preparation. A living muscle taken from an 

 animal has been attached to a light lever, the end of 

 which makes a scratch on a piece of smoked paper. 

 The paper is fastened on a revolving cylinder and so 

 long as the muscle is motionless the end of the lever 

 marks a horizontal line on the paper. But if the 

 muscle is stimulated so that it contracts and then re- 

 laxes again the lever is pulled up and is then lowered, 

 and so its point makes a curve on the paper. The 

 nerve going to the muscle can be stimulated electrically 

 and the moment of the stimulation can be recorded by 

 another lever, which makes a mark on the paper below 

 the trace made by the lever which is attached to the 

 muscle. Two such shocks have been applied to the 

 nerve and they have elicited two contractions of the 

 muscle and these two contractions have fused together. 



In the actual experiment the operators could see 

 that the muscle moved, and they could feel that a 

 certain interval of their own duration coincided with 

 the interval between the first and second depressions 

 of the key that made the electric shocks. But the 

 extent of motion of the muscle was too small, and the 

 depressions of the key succeeded each other too rapidly 

 to be easily observed, and therefore all these events 

 were made to record themselves on the myogram. 

 The series of little notches at the base of the figure 

 represent the movements of the time-lever, that is, 

 they are scratches made on the paper by a little lever 

 which moves up and down at a rate fixed beforehand. 

 Now when this time lever had made ten notches on 

 the paper the first shock was applied to the nerve, 

 and at the eleventh the muscle began to contract. 

 At the seventeenth notch the second shock was applied 

 and the muscle continued to contract. At the twenty- 



