( 393 ) 



of the mutual removal of the neigiibouring dermafomata, will be 

 exposed moreover, in consequence of the more important operation, 

 to a greater \ariability of shape, and we must be prepared to obtain 

 only caricatures of its real shape. 



In order however to undertake a just evaluation of these carica- 

 tures, it is necessary to know beforehand the variations in shape, 

 suffered for the same reasons by the trunkdermatomata. A knowledge 

 of the significance of the dorsal, lateral and ventral portions of the 

 dermatoma, of their maxima and of their different reactions on a 

 more or less serious trauma, is needed to enable us to understand 

 the caricatures, obtained on the extremities. Even the technical 

 mastership of Sherrington has not wholly succeeded, we believe, 

 in interpretating them truly. 



The second difficulty, the perfect control of which we owe to 

 Sherrington, is found in the individual variations, presented by the 

 animals experimented upon. On all dogs it is not always the same 

 dermatomata that participate in the covering of the extremity. In 

 most cases it will be the 5^*^ — 11^^ posterior roots that participate 

 in the innervation of this extremity, vet it may sometimes occur 

 that the 4''' — 10''' (in cases of so-called pre-fixion), or also the 

 (3ih — 22^'' (in cases of post-fixion) take their place. For this reason 

 we cannot always be sure of the equivalence of two roots situated 

 at the same height. The 9^'^ root e.g. may (in cases of pre-fixion) 

 take up the part generally performed by the IQi^'', or (in cases of 

 post-fixion) that generally performed by the 8^'' etc. 



Even if one is prepared by a previous knowledge of the trunk- 

 dermatomata for a true interpretation of the caricatures, and knows 

 the dangers arising from pre- and post-fixion, it will still be necessary, 

 as it has been done by Sherrington, to describe the consequences 

 of every separate isolation in the same manner, in order to retain 

 one identical point of view for all of them. 



In order to find this point of view, we have thought it convenient 

 to adopt for the extremities mid-dorsal and mid-\entral lines, in the 

 same ^^■ay as had been done already by Bolk and Sherrington; 

 moreover we made use of a simple artifice. 



As soon as a dermatoma has been isolated on an animal, employed for 

 our experiments, and the boundaries of the insensible zones have been 

 defined on the skin, the animal is photographed in different attitudes. 

 When by these preliminaries Ave have obtained the photos necessary 

 for controlling the experiment, the animal is killed, and the skin 

 with the designs upon it, after having been iwe pared further in a 

 deHnite methodical manner, is tanned and stretched, in order that it 



