76 



SCIENCE 



[N. S. Vol. XXXIX. No. 993 



determine whether a gradient would appear ij, 

 the structural death changes. A number of 

 nerves were observed in various concentra- 

 tions of KON from 0.001 m. to 0.01 m. In 

 these solutions the fibrillffi become after a 

 time irregular in outline and more or less 

 varicose so that the strand appears more or 

 less granular instead of fibrillar like the fresh 

 living nerve. The preparations showed some 

 indications of the progression of the change 

 from the central to the peripheral end of the 

 nerve, but the changes were so slight that the 

 possibility of a subjective factor being con- 

 cerned could not be neglected. In the at- 

 tempt to obtain more distinct structural death 

 changes other narcotics were used, and it was 

 found that in ethyl ether the fibrillation al- 

 most completely disappeared and the strands 

 became very distinctly granular in appearance 

 in consequence of irregular swelling and 

 varicosity of the fibrils. In 1 per cent, ether 

 or somewhat lower concentrations these 

 changes occur, slowly requiring several hours 

 for completion, and a very distinct gradient in 

 their occurrence is visible. The change from 

 fibrillar to granular appearance begins at the 

 two ends of the nerve very soon after it is 

 broiTght into the solution, and a distinct gradi- 

 ent in this change can be seen extending a 

 few millimeters peripherally from the central 

 end and a shorter distance centrally from the 

 peripheral end. This first change remains 

 limited to the two terminal regions of the 

 nerve and is undoubtedly associated with the 

 stimulation and injury resulting from sever- 

 ing the nerve at these two points. 



Later, however, the change begins to pro- 

 gress along the nerve from the central toward 

 the peripheral end, but the change at the 

 peripheral end progresses only very slowly or 

 not at aU in the central direction. From this 

 time on a distinct gradient in the change is 

 visible until it has progressed along the 

 whole length of the nerve. Except in the ter- 

 minal region adjoining the peripheral cut end 

 the death change always progresses in the 

 peripheral direction. The peripheral third of 

 the length may be entirely unchanged at a 

 time when the central third or more has com- 



pletely lost its fibrillar appearance. When 

 long strands are so arranged that central and 

 peripheral regions are side by side in the 

 same field of the microscope the differences 

 between the two regions are very striking. If 

 the nerve is crushed or injured at any point 

 short gradients appear on both sides of the 

 injury, but do not extend to any great dis- 

 tance before the general change reaches this 

 region in its progress peripherally. 



The existence of this centro-peripheral 

 gradient in the death changes of the nerve 

 fiber in narcotics must mean that a gradient 

 of some sort exists in the living nerve and if 

 the action of the narcotics is of the same 

 character here as in other cases we must con- 

 clude that this gradient is associated with 

 metabolism and that the rate of metabolism 

 or of certain metabolic processes is in general 

 higher at the central end and decreases 

 peripherally in this nerve. 



That metabolic gradients occur very widely 

 it not universally, at least during the earlier 

 st ges of development in axiate organisms 

 a ' structures, is evident from the data of 

 ei bryology. The so-called law of antero-pos- 

 ter or development must be the expression of 

 an axial metabolic gradient. And as regards 

 plants there is a large body of evidence which 

 indicates that the vegetative tip possesses a 

 higher rate of metabolism than other regions 

 of the same axis. Even in the unicellular 

 body of the ciliate infusoria and in various 

 other cells which show a morphological polar- 

 ity the writer has observed a susceptibility 

 gradient. In view of the facts it is impossible 

 to doubt that such gradients are in some way 

 closely associated with polarity in organisms, 

 and various lines of experimental evidence 

 which can not be considered here indicate that 

 they constitute the dynamic basis of polarity. 

 There are, moreover, many facts which suggest 

 that the establishment of a gradient of this 

 kind is the first step in individuation in 

 axiate organisms. 



C. M. Child 



Hull Zoological Laboratort, 

 University of Chicago, 

 Chicago, III. 



