LATENT PERIOD. 215 



it. They must write on the same vertical line. Make these 

 adjustments on the paper close to the overlap so as not to 

 encroach on valuable space. Remove the points from contact 

 with the paper by turning the pillar arm : the points will 

 fall back into position when the arm is again brought up to 

 the stop. 



6. Take a record. Start the style by closing its key ; start 

 the drum, let it run round three times so that it may settle 

 to its speed ; open the S key, note if the muscle gives a good 

 contraction, and if its does, apply the points to the paper 

 the moment that the guide mark comes into view, and lift 

 them off again on its next appearance. The record thus lasts 

 for one revolution only. 



Examine the curve : The muscle, if unfatigued, will record 

 an even sweep upwards to a summit and a symmetrical fall. 

 The lever will not return at once to the line from which it 

 originally started, but after the first symmetrical fall will 

 exhibit a slower contraction remainder. This is not always 

 a smooth descent, but frequently consists of several oscillations, 

 the first of which falls below the abscissa to rise above it 

 again. This may be repeated several times in very vigorous 

 muscles. They disappear with fatigue. Should the upstroke 

 of the curve show an indentation on its ascent or a double 

 crest, the drum contact is at fault and should be reset, 

 because the opening shock has been delayed through the 

 length of the contact, and two separate stimulations are being 

 produced. 



7. Measure the latent period. Turn the style aside to 

 prevent it writing, and replace the muscle lever in contact 

 with the paper at the beginning of the tracing. Carry an 

 abscissa beneath the whole length of the former. Lift the 



