MUSCLES. 479 



which lines them, as in the case of the heart and blood-vessels, the 

 alimentary canal, and other hollow muscles, nor does light act 

 upon the iris but upon the retina, arid the influence of emotions, 

 sudden or continued, on the action of all involuntary muscular 

 parts, whether large, like the heart and as in the alimentary 

 canal, or minute, as in the capillary vessels, must be communi- 

 cated by nerves. Some vivisectors say that a stimulus applied 

 to the nerves of an involuntary part do not excite it; others 

 assert the reverse. But any stimulus applied to a nerve belong- 

 ing to a voluntary muscle, mechanical or pungent, heat or elec- 

 tricity, excites it instantly to action, and will excite it after 

 pricking or cutting the fibres themselves has ceased to produce 

 contraction. 6 Stimulation still further back, of certain parts of the 

 chorda spinalis or oblongata, or of the brain, has the same effect. 

 Division of the nerves or spinal chord, great compression, dis- 

 integration, any thing which prevents continuity of influence 

 from the brain to the termination of the nerve in the muscle, 

 destroy the power of the will. The contractility of the 

 muscle is of course unimpaired ; it contracts equally as before, 

 if a stimulus is applied to it or to the portion of the nerve 

 connected with it. Yet, some contend that the very power of 

 contraction depends upon nerves. They adduce the influence of 

 poisons, applied to the nerves, in destroying the irritability of 

 muscles to which they are distributed, and declare that, even if 

 strong poison is applied to the nerves of muscles detached from a 

 living animal, the muscles cannot afterwards be excited, f But 

 Fontana discovered that the portion only of the nerve that has 

 been in contact with alcohol is incapacitated from conveying 

 stimulus ; so that, if the stimulus is applied to the nerve farther on, 

 the muscle contracts as at first, s Even had not Fontana made 

 this discovery, the effect could have been ascribed to the trans- 

 mission only of the effects of the poison along the nerve, and 

 could, like the effect of mechanical and all other irritation of 

 the nerves upon muscles, have shown only the connection and 

 influence between the two. Dr. Whytt discovered that, if an 

 animal is poisoned by opium, the effects pervade the system much 



e Whytt. Physiol. Essays, ed. 2. 1761. p. 249. Sensibility. 

 f Dr.Bostock. Elemen. Syst. of Phys. ed. 3. p. 179. Dr. Tiedemann, ccccxlii. 

 This was fully confirmed, in regard to other narcotics, by Dr. C. Henry, 

 Edinb. Med. and SurgicalJournal, 1832. No. CX. p. 17. 



K K 



