428 SCIENCE PROGRESS 



Dr. Kennedy's own records supports the same view. In three 

 of his four cases sensation returned first in the parts nearest 

 the suture, and later in more distant parts, such as the finger 

 tips. This surely proves that regeneration was occurring in 

 a peripheral direction. The record of the fourth case gives 

 no details of the order of recovery. The only difficulty 

 remaining is the unusual rapidity of the reparative process. 

 I say " unusual " because most of our ideas of the rate at 

 which axis cylinders grow are derived from cases in which 

 gross impediments to growth are present. I have, however, 

 been struck in some of our own observations with the rapidity 

 with which the central unites with the peripheral end, even when 

 an inch or more of nerve has been excised. In some cases 

 there was a well-defined strand of union after a few days. This 

 is especially the case when young and vigorous animals are 

 employed. In two of Dr. Kennedy's cases, the patients were 

 in the prime of life (aged twenty-nine and thirty-seven re- 

 spectively) ; the other two were children — aged six and sixteen 

 respectively. 



The introduction of the new methods of Cajal has now 

 furnished us with a method of tracking the growing axis 

 cylinders with a certainty which was previously lacking ; and 

 Marinesco, availing himself of these methods, has shown that 

 the lengthening of the regenerating fibres is demonstrable 

 twenty-four hours after a nerve has been cut. 



This concludes what I have to say on an important problem 

 of what we may call applied physiology. In the present state 

 of our knowledge it is impossible to avoid controversial 

 questions. The proverbial disagreement between doctors is 

 specially true of physiologists, and really this is only as it ought 

 to be. Whilst knowledge is in the making there must be 

 divergencies of opinion, and it is only by a full and free dis- 

 cussion of these, and by the renewed research of which criticism 

 is the stimulus, that any certainty in the way of truth can be 

 arrived at. 



