president's address. 23 



supports what may be called the qualitative theory. I am not competent 

 to form an opinion on the subject, but I confes.s to being impressed by 

 Bering's argument that the nerve-cell and nerve- fibre, as parts of one 

 individual (the neuron), must have a common irritability. * On the other 

 hand there is striking evidence, in Langley's ^ experiments on the cioss- 

 grafting of efferent nerves, that here at least nerve impulses are inter- 

 changeable and therefore identical in quality. The state of knowledge as 

 regards afferent nerves is, however, more favourable to my point of view. 

 For the difficulties that meet the physiologist — especially as regards the 

 nerves of smell and hearing — are so great that it has been found simpler 

 to assume differences in impulse-quality, rather than attempt an explana- 

 tion of the facts on the other hypothesis."^ 



On the whole it may be said that, although the trend of physiological 

 opinion is against the general existence of qualitative differences in nerve- 

 impulses, yet the question cannot be said to be settled either one way or 

 the other. 



Another obvious difficulty is to imagine how within a single cell the 

 engrams or potentialities of a number of actions can be locked up. We 

 can only answer that the nucleus is admittedly very complex in structure. 

 It may be added (but this not an answer) that in this respect it claims no 

 more than its neighbours ; it need not be more complex than Weismann's 

 germ-plasm. One conceivable simplification seems to be in the direction 

 of the pangenes of De Vries. He imagines that these heritage units are 

 relatively small in number, and that they produce complex results by 

 combination, not by each being responsible for a minute fraction of 

 the total result. 3 They may be compared to the letters of the alphabet 

 which by combination make an infinity of words.'' Nitgeli * held a 

 similar view. ' To understand heredity,' he wrote, ' we do not need a 

 special independent symbol for every difference conditioned by space, 

 time, or quality, but a substance which can represent every possible com- 

 bination of differences by the fitting together of a limited number of 

 elements, and which can be transformed by permutations into other com- 

 binations.' He ajiplied {loc. cit., p. 59) the idea of a combination of 

 symbols to the telegraphic quality of his idioplasm. He suggests that as 

 the nerves convey the most varied perceptions of external objects to the 

 central nervous system, and there create a coherent picture, so it is not 

 impossible that the idioplasm may convey a combination of its local altera- 

 tions to other parts of the organism. 



Another theory of simplified telegraphy between soma and germ-cell 



'Pm-. It. Soe., 1904, p. 99. Journal of Physiology, xxiii. p. 240, and xxxi. 

 p. 365. 



'■^ See Nagel, Handbuch der Fhysiologic des Menschen, iii. (1905), pp. 1-15. 

 ' De Vries, Intracellular Pangenesis, p. 7. 



* I take this comparison from Lotsy's account of Do Vries' theory. Lotsy, 

 I'orlesungen ilber Deszendenztheorien, 1906, i. p. 98. 



* Nageli's Ahstammungslehre, 18S4, p. 73. 



