104 FOURTH REPORT — 1834. 



scribed, without inventing others unwarranted by experience. 

 On this principle he instituted innumerable experiments to dis- 

 cover and illustrate the properties of the vital powers. He proved 

 the existence of a property in muscle, to which he restricted the 

 term irrituhiliti/, which is only called into action by means of 

 stimuli, which affects a much greater vivacity of motion than 

 mere elasticity (a property of dead matter), the motions also con- 

 sisting in alternate oscillations, with contraction, swelling, and 

 wrinkling of the fibre, followed by extension, relaxation, and 

 elongation of the same. He further attributed to the muscles a 

 nervous power, distributed to them from the brain by means of 

 the nerves, as a necessary condition of their irritability *, but 

 which entirely diJTers from it. He concluded from his experi- 

 ments, as detailed in his earlier works, that the following parts 

 are destitute of irritability and nervous power : periosteum, peri- 

 toneum, pleura, ligament, tendon, articular capsules, the cornea, 

 parenchyma of the viscera. In these tissues he admitted a force 

 analogous to elasticity, inherent in their organic texture, which 

 solicits them to contract slowly M'hen divided, when exposed to 

 cold, &c., and which only abandons them when entirely disorgan- 

 ized. He proved that sensibility is inherent in the nerves, but 

 that they are destitute of irritability. He denied that irritability 

 could be imparted to the muscles by the nerves, because, seeing 

 that a nerve, un being stimulated, may excite motion in the muscle 

 to which it passes, but offers not the slightest motion itself, it is 

 impossible to suppose they shovild be the source of that to others 

 which they never possessed themselves ; and, more particularly, 

 because he perceived that the excitement of muscles through 

 nerves is a pheenomenon not true of all, but only of certain, 

 muscles. 



He proved, universallj^, that irritability resides in all parts 

 that have muscular fibre ; that this power differs in intensity 

 and permanence in various parts ; that these qualities are most 

 observable in the heart, more in the left ventricle than the 

 right ; that next in order come the intestines, the diaphragm, 

 the voluntary muscles. From reiterated experiments he concluded 

 that the heart and other involuntary muscles are not excited to 

 contract by stimulating the nerves with which they are supplied, 

 but that they require specific stimuli ; thus, that the blood is to 

 the heart what the Avill is to the voluntary muscles. 



• Si insita eonim organonnn (cordis, intestiiiorum, &c.) vis est, cur accipiunt 

 nervos? li, nisi voluntatis imperia atferunt, quid aguiit aliud ? Primo sensum 

 aflerunt, qui absque nervis nullus est. Adferunt etiam ex cerebro efficaeia im- 

 peria non voluntatis, sed legum, corpori aniniato scriptannn, quae volunt, ad 

 certos stiimilos ccrtos nasci motus. — Elem. PI'ys., toni. iv. p. 516. 



