to the Agency of the Nerves. 117 



the heart ; an infusion of tobacco applied to the brain diminishes 

 it. We may admit that galvanism is a power capable of pro 

 ducing both these kinds of effect on muscular organs, according 

 as it is applied in a greater or less degree of intensity ; but have 

 we any reason to suppose, either that these two substances, act- 

 ing on nervous matter, can excite galvanism at all, or that they 

 can excite it in so very various degrees of intensity ? 



These considerations seem sufficient to shew, that we cannot 

 suppose the action of nerves on muscles to be of the nature of 

 galvanism, without supposing a much greater variety in the 

 modes of exciting galvanism, and, in its effects on muscular 

 organs, than any observations on this power entitle us to 

 assume. 



3. If we suppose, with the authors of the galvanic theory 

 of nervous actions, that these actions are essentially concerned 

 in secretion, a strong argument against their identity with 

 galvanism arises from the fact, that the various secreted fluids 

 are so different from each other. This difficulty increases 

 greatly, when we take into account the nutrition of all the dif- 

 ferent textures in the body, a process which Haller has well 

 characterized as " omnium amplissima secretio." If there 

 be powers in the animal economy distinct from galvanism, 

 which are sufficient for the formation of the solids of the ani- 

 mal body, out of the blood, it is quite obvious that these powers 

 must be amply sufficient for the formation of the secreted ^mw/s 

 out of the blood, and it is therefore quite unnecessary to suppose 

 galvanism concerned in this last process. But if we regard 

 both secretion and nutrition as dependant on galvanism, trans- 

 mitted through the nerves, and refer to this cause the forma- 

 tion of all animal substances, from bone to serum, out of the 

 blood, then, I think, we must make one of two suppositions. 

 Either we must suppose the galvanism transmitted by the 

 nerves to the various parts of the body, to be different in its 

 nature in different places ; or we must suppose the blood to 

 undergo very various preparation in the different parts of the 

 body, before it is submitted to the action of the galvanism. 

 In the former case, our explanation is contradicted by all 



