CHAP. 1.] OF PROPER SENSATION. 57 



which the change excited by the stimulus at one part of the nerve 

 is conveyed throughout its course to the muscle, or to the brain or 

 other nervous centre, with which it may be connected, producing 

 in them the same or an analogous state. 



As these phenomena occur in tissues, whose chemical composi- 

 tion is more complex than that of any others in the body, and 

 which are the seat of continual changes, they are subject to many 

 disturbing causes, and are easily affected by slight modifications in 

 the general state of the system. Many substances quickly exert 

 an influence upon them, as opium, strychnine, and various seda- 

 tives, narcotics, or stimulants. Those properties are therefore en- 

 tirely dependent on the nutrition of their respective tissues ; they 

 quickly vary with the state of that function, and when it ceases, in 

 death, they vanish with it.* 



* For information upon the subjects treated of in this chapter we refer to 

 the following sources : Henle, Algemeine Anatomic ; Berzelius. Chimie Or- 

 ganique, Fr. edit. 1833 ; Prout on Stomach and Urinary Diseases ; Liebig's 

 Animal Chemistry, by Gregory ; Graham's Chemistry ; Daniell's Chemistry ; 

 Schwann, Mikroskopische Untersuchungen iiber die Uebereiustimmung in 

 der Struktur und deni Wachsthum der Thiere und Pflanzen ; Dutrochet, ar- 

 ticle Endosmose, in the Cyclopaedia of Anatomy and Physiology. 



