2l6 DYNAMICS OF LIVING MATTER 



ing smaller chela originally had. Thus the animal is normal again, but 

 the relative position of the two chelae is now reversed. If later on in 

 such an animal the larger chela is cut, the original order can be obtained 

 again. 



E. B. Wilson has repeated the experiments of Przibram, and made 

 the important discovery that the growth of the smaller chela after the 

 removal of the larger one does not occur if the nerve of the former is 

 previously cut.* The number of the successful operations w T as small, 

 but the results were significant. This brings Przibram's experiments 

 into a line with Herbst's and Morgan's. 



It seems to follow from these facts that the nerves have a function 

 which is different from that of a mere conductor of stimuli; namely, 

 that of causing the growth or development of certain organs. It has been 

 argued that these two functions are not different, inasmuch as in both 

 cases the nerve acts only as a conductor of stimuli and that these stimuli 

 determine the phenomena of regeneration mentioned here. Child ex- 

 presses such a view, and Herbst's idea of " formative stimuli " is only a 

 somewhat less definite expression of the same view. It seems to me that 

 there exists a still different possibility ; namely, that the nerve may also 

 act as conductor for certain substances which go from the periphery 

 to the ganglion cells or in the reverse direction and are carried through 

 the axis cylinder. Especially the observations of Lewis and possibly 

 those of Herbst and Przibram suggest such a possibility. But before 

 we admit the possibility that the axis cylinder can act as a conductor 

 for the passage of definite substances, we must look for facts which war- 

 rant such an assumption. Such facts are given by the beautiful dis- 

 covery of Hans Meyer f that the tetanus toxin is carried from the wound 

 to the central nervous system through the axis cylinder of the nerves, 

 and neither through the blood vessels nor the lymphatics nor the sheaths 

 of the nerves. It is hardly necessary to emphasize the fact that through 

 this discovery an entirely new light is thrown upon the role which the 

 nerves or ganglion cells may play in the phenomena of regeneration. 

 The possibility now arises that the axis cylinder may act as a conducting 

 path for certain substances which in some animals may be necessary 

 for the starting of a process of regeneration or which may modify the 

 nature of the organ which is to be regenerated. 



A few words may finally be said about the well-known effects of 

 certain organs like the hypophysis and the thyroid gland on phenomena 

 of growth. Certain parts of the body - - namely, the lower jaw, the 



* E. B. Wilson, Biological Bulletin, Vol. 4, p. 197. 



f Hans Meyer, Festschrift fur Jaffe, 1901. Meyer und Ransom, Archiv fur Expcrim. 

 Pathol. und Pharmacol., Vol. 49, p. 369, 1903. 



