322 



NERVOUS SYSTEM. 



the cavity of the thorax is enlarged so as to admit of the intro- 

 duction of air, evidently depends upon the phrenic and the in- 

 tercostal nerves. If the nerves which supply the structure of 

 the lungs be alone intercepted, as the par vagum, either by liga- 

 ture or section, the changes on the blood produced by respiration 

 cease, and the animal dies. 



Secretion, exhalation, absorption, and animal heat, seem also 

 to be dependent upon the integrity and the activity of nervous 

 influence. The action of the heart, sensation and voluntary mo- 

 tion, are in the same predicament. 



The manner in which these several kinds of innervalion is 

 produced, is unintelligible. One has supposed it to consist in a 

 vibration of the elementary fibres of the nerves; another in an 

 agitation of their elastic globules; another in the transmission of 

 an imponderable fluid, as ether, magnetism, electricity, and Gal- 

 vanism. Reil has proposed, on this subject, what has been 

 termed a chemico-vital hypothesis: according to him, the ge- 

 neral action of parts depends upon their form and composition; 

 consequently, when the two latter vary, the first does also. M. 

 Beclard* inclines to the opinfon, that "the nervous system is 

 the elaborator and conductor of an imponderable agent; and, 

 like electricity or magnetism, that by it we can explain all the 

 phenomena of innervation: The relation between the benumb- 

 ing influence of electric fish and Galvanic phenomena on one 

 part, and ordinary nervous action on the other ; The practica- 

 bility of causing Galvanic phenomena by the nerves and 

 muscles alone; The possibility of producing muscular con- 

 traction, the chymifiant action of the stomach, the respiratory 

 action of the lung, &c., in substituting a Galvanic for a ner- 

 vous influence ; The existence of a nervous atmosphere, ac- 

 ting at a distance around the nerves and muscles, and between 

 the ends of divided nerves; The wrinkling of muscular fibres 

 in contraction, and the relation of the finest transverse nervous 

 fibres with those wrinkles, are phenomena of innervation which 

 nearly approach certain electro-magnetical ones/' 



This subtile fluid, according to M. Beclard, seems to be formed 

 every where, but principally in places where there is much 

 vascularity along with the ash-coloured substance. It impreg- 



* Anat. Gen. 



