494 



PRINCIPLES OF GENERAL PHYSIOLOGY 



neurones, in addition to the muscle fibre at one end and the receptor organs in 

 the skin at the other end. Where in this series are we to place the seat of the 

 refractory period ? Now, when the motor neurones, made use of by this reflex, 

 are excited for a different reflex from receptors in the leg itself, this refractory 

 phase does not show itself ; the flexion reflex is a steady one. We can exclude, 

 therefore, the motor neurones of the final common path, as well as the muscles 

 themselves. We have seen above that there must be some mechanism common 

 to impulses started at two different spots in the receptive area, even when they 

 are 10 cm. apart. There is, further, no evidence that there is any direct con- 

 nection between receptor neurones themselves ; there is only that due to their 



synapses with other neurones common to both 

 receptors. The conclusion is that the refractory 

 period must be in some neurones on the afferent 

 side of the motor neurones of the final common 

 path, a conclusion which, indeed, seems to be 

 necessary for the proper working of the reflex 

 mechanisms; since the rhythmic movement of 

 scratching would not do for the other reflexes in 

 which the same motor neurones take part. It is 

 interesting to note that the rate of the rhythm is 

 almost identical with that observed by Gotch and 

 Burch (1896) in the discharge of the electrical 

 cell of Malapterurus. 



RECIPROCAL INNERVATION 



When there arc two sets of muscles acting on 

 a movable organ, such as the eye or a part of a 

 limb, in such a way that they antagonise one 

 another, it is clear lhat, for the effective per- 

 formance of a particular reflex movement, any 

 contraction of the muscles opposing this move- 

 ment must be inhibited. Further, the inhibition 

 of the one group must proceed pari passn with 

 the excitation of the other group to ensure a 

 well-controlled and stead}' motion. 



This fact was obvious to Descartes (1677), and 

 Figs. 154 and 155 are taken from his treatise 

 " De THomme." 



The history of this work is of some interest. Refer- 

 ences are usually made to the Latin translation, " De 

 Homine," but, happening to come into possession of an 

 edition in French brought out by Descartes' friend and 

 disciple, Clerselier, I wondered why the original French 

 manuscript of the author had been translated into Latin 

 and then, apparently, back again into French. On 



investigation, I found that Descartes, having the fate of Galileo before him, was by no means 

 desirous of offending the ecclesiastical authorities, so that the work remained unpublished 

 at his death in 1650. Clerselier had one copy of the manuscript and another copy was 

 translated into Latin by Schuyl and published at Leyden in 1662. Clerselier, hearing of 

 this, hastened to publish the original French manuscript in Paris. In the second edition, of 

 1677, he apologises for some errors which, owing to the hurried publication of the first edition, 

 had crept in. So that his second edition appears to be the most accurate representation of the 

 original. 



Descartes left some extremely rough sketches, one of which, as copied by Clerselier, "with 

 his best ability," as he says, is given in Fig. 155. The figures with the letter G at the bottom, 

 reproduced in Fig. 154, are by a M. Gutschoven of Louvain. Clerselier made the acquaintance 

 of this gentleman and, finding him to be thoroughly familiar with the views of Descartes from 

 his conversations with the philosopher, commissioned him to draw more figures in order that 

 the text should be more easily understood. A further series of drawings were obtained from a 

 M. de la Forge, whose notes were also added to the book. I have not thought it necessary, to 

 reproduce M. de la Forge's figure. 



The description of the figures is sufficiently interesting to give it in Descartes' own words 

 and I think that it must be admitted that Gutschoven's diagram makes them more intelligible : 



Fin. 155. DESCARTES' ROUGH 



SKETCH OF THE INNERVATION 

 OF THE EYE MUSCLES. 



(Descartes, 1677, p. 16.] 



