OP THE NERVOUS SYSTEM IN GENERAL. 473 



The most limited instinct, which, in all animals, even the 

 most imperfect, necessarily connect certain motions with cer- 

 tain sensations, is also a nervous action. 



Sensation and volition, whatever may be the intermediate 

 phenomena, are still actions of the same kind. 



The phenomena of irritation, that is to say, impression not 

 perceived and involuntary motion, are themselves more or 

 less dependent on nervous action. In the intestinal canal, in 

 the heart, &c., usually the impression is not perceived, and 

 the muscular contraction is not voluntary, but notwithstand- 

 ing the nervous system intervenes; for if in the regular order 

 the impression does not pass beyond the ganglions, and if the 

 muscular contraction is the necessary consequence, which is 

 the character of irritability, in certain cases of extraordinary 

 impressions, sensation results; also when the will is troubled 

 by the passions, the interior muscular movements are per- 

 ceived. In the vessels, and especially in the arteries, the 

 nervous action is very evident. In the cellular tissue the 

 impression and the contraction closely connected, and desig- 

 nated by the single name of tonicity, appear to be slightly 

 dependent on the nervous system, but however are not alto- 

 gether foreign to it. 



The nervous influence is not limited to the organs or solid 

 parts alone, the blood* experiences its effects. 



756. The nutritive and genital functions, also, are all more 

 or less dependent on nervous action. 



Digestion,! not only the sensations and motions which take 

 place at the entrance of its organs, but even the action of the 

 stomach, is obedient to the nervous action; it has been known 

 for a considerable time that the section of the nerves of the 

 stomach deprives this organ of the faculty of digesting and 

 pushing forward the aliment into the intestines. 

 Respiration is not less dependent on nervous influence; the 



* G. A. Treviranus, Biokgia, B. 4, page 646. Idem, Fermischte Schriften, 

 &c. B. I., page 99. 



j- A. Brunn, Experim. circa ligat. nervorum. Vavasseur, de 1? influence du 

 systeme nerveux sur la digestion stomacak: These. Paris, 12. aout. 1823. 



