Herrick, Anenccphalas and Amyelus. 5 



less extent. The body is a vital unit and any attempt to re- 

 vive the Cartesian notion of a dominant central directive force 

 which governs despotically the activities of growth and normal 

 physiological function is a step backward. Whenever a physi- 

 ological union is to be instituted between one part of a grow- 

 ing embryo and another part, the impulse from one side is met 

 by a reaction from the other. This is well illustrated in the 

 development of the sensory ganglia by the fact that cotempo- 

 raneous with the centrifugal ganglionic outgrowth there is a 

 thickening of the epidermis of the corresponding region and it 

 requires both of these elements to form the completed ganglion. 

 Hereditary cell-forces are in operation on both sides ; and fur- 

 thermore unless these forces are both kept operative throughout 

 life there will inevitably be degeneration, as is shown by the 

 atrophy of the primitive embryonic sensory ganglia of the first 

 segments of the head region, the degenerations following ampu- 

 tations, etc. 



To return to Professor v. Leonowa's paper, he calls attention 

 to the fact that this case is a confirmation from a third point of 

 view of Waller's law. This law in its most general form states 

 that after section of a nerve degeneration follows the customary 

 path of the stimulus and proceeds in the direction of the stimu- 

 lus. This was based upon experimental researches. His and 

 many others after him have shown by purely embryological 

 methods that the embryonic growth is in the same direction ; 

 and now we have even stronger evidence from the side of 

 pathology. 



Waller's law, however, is completed by the following facts ; 

 ( 1 ) Section of sensory and motor roots between the ganglion 

 and the cord is followed by the atrophy of both of the roots 

 remaining connected with the cord ; ( 2 ) Section of the root 

 between the ganglion and the periphery causes the destruction 

 of the peripheral part and of the ganglion also. These obser- 

 vations apparently contradictory to Waller's law do not essen- 

 tially alter it, for according to recent researches the destruction 

 of the ganglia, the atrophy of the motor fibres, the destruction 

 of the motor cell of the ventral cornu of the cord, all result 



