Nervous System. 547 



not the power which performs the contraction, it only sets it off. And 

 likewise the passage of the stimulation from the point touched to other 

 points at a distance, only touches off a force already there. The track 

 traversed by the stimulation represents the track of a system of nerves 

 not yet developed. When they are developed, as we find them in ani- 

 mals of higher organization, they are still merely the pathways of stim- 

 ulations which do not furnish the chief power, but simply regulate its 

 demonstrations. Now this regulation of the movement of an organ 

 may come from any one of several sources, all of which together con- 

 stitute its environment. The lungs may be made to move faster by a 

 strong emotion and also by the will. In either case the path of the 

 stimulation leads from the brain. They can also be caused to go faster 

 after violent exertion or by the exhaustion of disease, in which cases 

 the stimulation is from the viscera by way of the sympathetic system. 

 Thus, whether the stimulation is from the animal part of the system or 

 the vegetative ; whether it is voluntary or involuntar3 r ; conscious or 

 unconscious, it is the same, and consists of a nervous current along a 

 differentiated route between two organs which have been developed in 

 relation to, and more or less dependent upon, each other. It was early 

 in animal development that a connection became established between 

 the animal parts locomotive, prehensile, &c. , and the vegetative parts, 

 stomach, &c. When the stomach is empty, the limbs and jaws must be 

 subject to its stimulation and be set to work to fill it. When it is full, 

 the stimulations from it to the animal organs cease, and these then cease 

 to furnish supplies. The distinction often made between mental and 

 physical stimulations is for convenience of study, and purely arbitrary. 

 Regardless of its origin the stimulation is physical only. In a great 

 many directions the influence of organs upon . each other is carried by 

 means of the sympathetic system alone, of the animal system alone, or 

 by means of both, and it is to be observed that the nervous electricity 

 is generated indifferently in both the animal and vegetative organs, and 

 that it is conveyed indifferently from the nerves of one system to those 

 of the other, backwards and forwards. There is no distinction in the 

 character of the influence which one organ possesses toward another, 

 no such distinction as mental and physical. 



The effect of the numerous ganglions and plexuses into which the 

 nerves run and convey their various currents, is to allow the modifica- 

 tion of such currents by their mutual action and reaction in reinforcing 

 or neutralizing, concentrating or dissipating, each other, &c. A current 

 coming upon a single nerve from a single organ, may, in a ganglion, be 

 split into two or more currents passing to as many different organs ; or, 

 coming from two or more, may be concentrated and continue from the 

 ganglion as only one. It has been long supposed by physiologists that 



