118 M. G. Cuvier's Report on the Researches 



2°. To what points of that system the impression must ex- 

 tend, in order to produce sensation. 



3°. From what points vohmtary irritation descends, and 

 what parts of the system ought to be untouched, in order to 

 produce it regularly. 



We will add, that in this first part he has considered these 

 questions only with relation to Vertebrated animals, and to their 

 nervous system of animal life ; that is to say, to the brain, the 

 spinal marrow, and the nerves which proceed from them. 



In order to resolve these questions, the author begins with 

 the nerves, and repeating, with respect to them, the known 

 experiments, he establishes the two general effects of their ir- 

 ritation which we have just described ; he shows with great 

 precision, that to produce contraction there must be a free and 

 uninterrupted communication of the nerve with the muscle ; 

 and that to produce sensation, a free and uninterrupted com- 

 munication with the encephalus is necessary: he concludes 

 that neither contraction nor sensation belongs to the nerve ; 

 that these two effects are distinct ; that they may be excited 

 independently of each other ; and that these propositions are 

 true, at whatever part, at whatever ramification of the nerve, 

 the communication may be intercepted. Employing the same 

 method with regard to the spinal marrow, he arrives at similar 

 results. When it is irritated at a certain point, it causes con- 

 tractions in all the muscles whose nerves originate below the 

 point of irritation, if the communications have remained free ; 

 it ceases to cause them if the communication is cut off". 



The exact inverse is the case with sensations; and as in 

 the nerves the empire of the will demands the same freedom 

 of communication as sensation does, the muscles below the in- 

 tercepted spot no longer obey the animal, and it no longer 

 feels them. Lastly ; if the marrow is intercepted at two points, 

 those muscles alone, whose nerves originate from the interval 

 comprised between those points, will experience contractions ; 

 but the animal has no longer any command over them, nor 

 does it receive any sensation from them. 



We shall not detail all the combinations by means of which 

 M. Flourens has varied the experiments on this subject ; it is 

 sufficient to say that they all lead to the result which we have 

 just described. 



The author concludes from them, that sensation and con- 

 traction do not belong to the spinal marrow any more than to 

 the nerves ; and this conclusion is decisive as it regards en- 

 tire animals. It would be very important to know, if it is 

 equally so as it regards animals which have lost the encepha- 

 lus, and which, in certain classes, appear to be far from losing 



immediately 



