G. GENERAL NATURAL HISTORY AND ZOOLOGY. 323 



a half long with a fish three fourths of an inch long in its 

 mouth. Their growth is very rapid, being as much as from 

 two to four inches in a month. The author having watched 

 some in a stream recently stocked with them, was able to 

 appreciate their increase in size from week to week. They 

 reached the length of five or six inches by autumn. Ger- 

 mantoion Telegraphy July 30, 1873. 



ORIGIN OF NERVE FORCE. 



Mr. A. H. Garrod has published an article in Nature upon 

 the " Origin of Nerve Force," in which, after referring to the 

 deficiency of our knowledge respecting the source of the 

 current which traverses the nerves, and is brought into play 

 through the instrumentality of its several parts, he states 

 that it is almost universally acknowledged that the current 

 itself is electricity in some form ; but whence it is derived few 

 have ventured to decide. The question is more difficult than 

 it would otherwise be from the fact that, in all those animals 

 which exhibit external electrical i^henomena to any extent, 

 as the Torpedo and Gymnotus, there are elaborate special or- 

 gans for the development of the shocks which they produce ; 

 but nothincr of this character can be detected in man or other 

 animals whereby an electrical current could originate ; and 

 although the brain and ganglia are often compared to the 

 batteries of a system of electric telegraph, how they could 

 act, if this were so, it is impossible to explain. The available 

 source of energy capable of giving rise to the nerve current 

 is yet unrecognized ; but this, according to Mr. Garrod, is to 

 be found in the differences of temperature between the in- 

 terior and the surface of the living body. This difference is, 

 itself, a source of power; and in hot-blooded animals there is 

 always a considerable discrepancy in that between the sur- 

 face and the interior ; there being a regulating action of the 

 skin, by Avhich a uniform internal temperature is maintained 

 in the latter, always hotter than the surface, whatever that 

 of the external medium may be. In cold-blooded animals, 

 the temperature of the interior is but slightly difterent from 

 that of the water or air in which they live; but that it must 

 be hio^her is evident from the fact that destruction of tissue 

 is continually going on in their bodies, which is always nec- 

 essarily attended with the evolution of heat. 



