23 



2d. The theories of Magendie and Flourens are also opposed, 

 by the fact that a slight puncture is sufficient to produce turning 

 or rolling. 



3d. As to the theory of Henle, which is based upon the 

 existence of convulsions in the eye, producing a kind of vertigo, 

 it has against it the facts that, on one side, convulsions may 

 exist in the eyes without any other disorder in the movements ; 

 and, on the other side, sometimes turning or rolling exist with- 

 out any convulsion in the eyes.* 



Nevertheless, I think that, in many cases, the vertigo conse- 

 quent on convulsions of the eyes is one element of the cause of 

 turning. I think also that, in certain cases, paralysis of some 

 parts of the body may facilitate the rotatory movements. But 

 their great cause, I think, is the existence of a convulsive 

 contraction in some of the muscles, on one side of the 

 body. These convulsive contractions are to be found in 

 every case of circulatory or rotatory movement. As to the cause 

 of these contractions, it exists in the irritation produced in cer- 

 tain parts of the encephalon. 



VI. ON A MEANS OP MEASURING DEGREES OF ANAESTHESIA AND 

 HYPER^STHESIA. 



The curious facts discovered by E. H. Weber, on tactile sen- 

 sibility, are well known. He found that if the two blunted 

 points of a pair of compasses are applied simultaneously on the 

 skin, there is, according to certain circumstances, either the 

 sensation of one or of two points. When the points are both 

 inside of certain boundaries, they are felt as one only ; 

 when they are outside of these boundaries, both are felt. 

 These boundaries vary exceedingly in different parts of the 

 skin, but for a given part the differences between men are 

 not extremely considerable. I have made use of the compasses 

 for measuring the degrees of tactile sensibility in diseases. In a 

 case of considerable anaesthesia of the lower extremities, the 

 patient only felt a single impression on one leg, although the 



* See a very remarkable case observed by my friend Dr. Lebret, in 

 Comptes rendus et Memoires de la Soc. de Biologic annee 1850. Paris, 

 1851. t. ii. p. 7. 



