THE PHENOMENON OF CONTRACTION. 



45 



ported by the results of artificial stimulation of the motor regions 

 of the brain. In experiments of this kind made by Horsley and 

 Schafer it was shown that, at whatever rate the stimulus might 

 be applied to the motor cells, they responded by motor discharges 

 of about 10 per second, so far as this could be determined from 

 the contractions of the muscle. The interesting conclusion from 

 the whole discussion, therefore, is that our motor centers, under 

 the stimulus of the will, discharge motor impulses at a certain low 

 rate, which, while somewhat variable, averages in ordinary move- 

 ments about 10 per second. 



The Ergograph. Voluntary contractions in man may be re- 

 corded in a great many ways, but Mosso has devised a special in- 



Fig. 22. Mosso's ergograph: c is the carriage moving to and fro on runners by means 

 of the cord d, which passes from the carriage to a holder attached to the last two phalanges 

 of the middle finger (the adjoining fingers are held in place by clamps) ; p, the writing point 

 of the carriage, c, which makes the record of its movements on the kymographion ; w, the 

 weight to be lifted. 



strument for this purpose, known as the ergograph. It has been 

 much used in quantitative investigations upon muscular work 

 and the conditions influencing it. The apparatus is shown and 

 described in Fig. 22. The person experimented upon makes a 

 series of short contractions of the flexor muscles of the middle 

 finger, thereby lifting a known weight to a definite height 

 which is recorded upon a drum. In a set of experiments the 

 rate of the series of contractions that is, the interval of rest 

 between the contractions is kept constant, as also is the load lifted. 

 Under these conditions the contractions become less and less ex- 

 tensive as fatigue comes on, and finally, with the strongest voluntary 

 effort, the contraction of the muscles is insufficient to lift the weight. 

 In this way a record is obtained such as is shown in Fig. 23 



