67 



thologists, this crossing takes place all along the medulla oblon- 

 gata, the pons Varolii, tubercula quadrigemina and the crura 

 cerebri. In all these organs there is truly a crossing of fibres, 

 but we do not know what are these fibres. Ch. Bell believes 

 that the crossing of the sensitive fibres takes place in the poste- 

 rior surface of the medulla oblongata, in a great part of the 

 length of the fourth ventricle. Longet supposes that this cros- 

 sing exists at the anterior border of the pons Varolii, where the 

 two processi cerebelli ad testes cross each other. 



My experiments prove that if there are some fibres coming 

 from the trunk and from the limbs which do not effect their 

 crossing in the spinal cord itself, their number ought to be very 

 small. Therefore the fibres which are found crossed in the ence- 

 phalon are not sensitive fibres coining from the limbs and from 

 the trunk, as all physiologists have supposed they were. 



My experiments were made on many different species ; 

 guinea-pigs, dogs, cats, sheep, and rabbits. In all the same re- 

 sults were obtained. 



To ascertain the degree of sensibility, I used various modes 

 of excitation ; mechanical, galvanic, physical, (i. e. warmth 

 and cold,) and chemical. I constantly compared the degrees 

 of sensibility in the parts of the body situated behind the in- 

 jured portion of the spinal cord, with the anterior parts of the 

 body, and particularly with the face. It is thus that I have been 

 able to ascertain the existence of an increase or of a diminution 

 in sensibility. 



Sometimes I have given chloroform to animals having had a 

 lateral half of the spinal cord divided in the cervical region. 

 I have found that complete loss of sensibility appeared at 

 first in the parts of the body opposite to the section of the spinal 

 cord, the head and neck, and at last in the parts of the body be- 

 hind the section of the cord, on the same side. This experiment, 

 as well as'many others, prove undoubtedly that there is an increase 

 of sensibility in these last parts. I will try in another article to 

 explain this hyperaDSthesia. 



I believe I am entitled to conclude from the facts above re- 

 lated : 



1st. That most of the impressions made on one side of the 

 body are transmitted to the sensorium by the opposite side of 



