THE P HAS IS OF FORCE. i8i 



The highest manifestation of animal life, however, is unques- 

 tionably that Nerve-force, by the instrumentality of which our 

 consciousness receives its impressions of phenomena external to 

 it, and our will exerts its power in producing motion through the 

 instrumentality of the muscular apparatus. Regarding the nature 

 of this force there is still some obscurity, but its very close rela- 

 tion to electricity cannot be doubted. Though many most eminent 

 physicists hold that they are identical, we regard the "correlation" 

 doctrine as equally accounting for all those facts which support 

 such a view, whilst it also accords with others which seem opposed 

 to it ; and we, therefore, prefer to consider nervous force as be- 

 longing to a distinct category. As its source lies, like that of 

 muscular power, in the chemical changes involved in the death 

 and decomposition of the peculiar tissue which manifests it, we trace 

 it back ultimately to the plant which generated the material of the 

 tissue, and thence to the light and heat which that plant received 

 from the sun. Although the most obvious exertion of this force 

 in the living body is that by which it calls forth muscular con- 

 traction, yet it can also influence in a very marked manner the 

 processes of nutrition and secretion ; so that its correlation with 

 the general organizing force is exhibited (as in the case of elec- 

 tricity and chemical action) on both sides, the nervous substance 

 giving up its characteristic organization whilst developing nerve- 

 force, and that nerve-force being transmitted to a distant part, to 

 be applied there in producing or modifying organization. It is 

 now well known that in the common experiment of exciting 

 muscular contraction by galvanizing a motor nerve, the galvanism 

 does not act directly through the nerve upon the muscle, but 

 excites the nerve-force in that part of the trunk which intervenes 

 between the point irritated and the muscle to which the nerve is 

 distributed ; and in like manner, when sensation is called forth by 

 the application of the electric stimulus to the sensory nerve, the 

 effect is produced, not by the transmission of the electric current 

 to the sensorium, but by the excitement of the nerve-force of the 

 part of the trunk which proceeds towards it from the point irri- 

 tated. And as the converse action to this excitement of nerve-force 

 by electricity, we have the excitement by electricity of nerve-force 

 in the electric fishes and a few other animals. Certain phenomena 



