174 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



in the words of the author as follows : " I conceive that the 

 various peripheral expansions of sensitive nerves take up un- 

 dulations or vibrations, and convert them into waves, capable 

 of being propagated along nervous tissue (neuricity, as it has 

 been named). Thust he same nerve tubule may be able to 

 transmit along it vibrations differing in character, and hence 

 give rise to different sensations ; and, consequently, the same 

 nerve tubule may, in its normal condition, transmit the wave 

 which produces the idea of simple contact, or that which pro- 

 duces the idea of heat ; or, again, the same nerve tubules in 

 the optic nerve which propagate the undulations of red, may 

 also propagate, in normal vision, those which excite the idea 

 of yellow or blue, and so for other senses. I advocate this 

 undulatory theory of sensation in preference to the theory of 

 distinct conductors : first, because it is simple ; second, be- 

 cause it is strongly supported by analogy when compared 

 with wave propagations in other departments of science ; 

 third, because it appears to be in harmony with a large num- 

 ber of recognized physiological facts, which seem inexplicable 

 upon the theory of distinct conductors." 5 A^July^ 329. 



MIND IX LOW^ER ANIMALS. 



Dr. Lauder Lindsay, in an essay which has excited some 

 attention, takes the ground that the mind of the lower ani- 

 mals does not differ in kind from that of man, and that they 

 possess the same affections, virtues, moral sense, and capacity 

 for education, and are liable to the same kinds of mental dis- 

 orders. 12 A, June 29, 169. 



EAPIDITY OF MENTAL TRANSMISSIONS IN A NERVE. 



Professor Helmholtz has made some new measurements of 

 the rapidity with which excitation is propagated along the 

 motor nerves of man from the brain to the muscles. The as- 

 certained rapidity of the excitation varies between 2G0 and 

 292 feet per second, and is also found to be greater in the 

 summer season than in winter. This result led to a more ex- 

 act observation of the influence of temperature, which was 

 ascertained by the artificial cooling or warming of the arm. 

 By this means the accelerating influence of a higher temper- 

 ature has been clearly determined, so as to show that the 

 interval of time between an impulse of the voluntary power 



