210 STRUCTURE AND ENDOWMENTS OF ANIMAL TISSUES. 



in consequence of the contraction of some neighbouring fibres, whilst 

 their own condition is that of relaxation. It may be artificially pro- 

 duced by bringing together the two extremities of a fasciculus, after 

 the irritability of the fibre has ceased ; so that the flexure at deter- 

 minate points must be owing simply to the physical arrangement of 

 the parts, perhaps to the passage of nerves or vessels in a transverse 

 direction. 



358. We have now to consider the conditions which are requisite for 

 the manifestation of Muscular Irritability. It has been already pointed 

 out, how close is the dependence of the property upon the due nutrition 

 of the tissue ; but the property cannot be long exercised except under 

 another condition, which is consequently of almost equal importance, 

 the circulation of arterial blood through the substance of the muscle. 

 The length of time during which the contractility remains, after the 

 circulation has ceased, has been shown by Dr. M. Hall to vary inversely 

 to the activity of the respiration of the animal. In co^-blooded animals, 

 the standard of whose respiration is low, the contractility remains for 

 many hours after death, even in the voluntary muscles ; and the muscles 

 of organic life retain it with great tenacity. Thus the heart of a Frog 

 will go on pulsating for many hours after its removal from the body ; 

 and the heart of a Sturgeon, which had been inflated with air and hung 

 up to dry, has been seen to continue beating, until the auricle had be- 

 come absolutely so dry as to rustle during its movements. An exceed- 

 ingly feeble Galvanic current is sufficient to excite the muscles of these 

 animals to contraction; so that Matteucci, in his experiments upon 

 Animal Electricity, has been accustomed to use the prepared hind-leg 

 of a Frog as the best indicator of the passage of an electric current. 

 Among ^arm-blooded animals, whose respiration is vastly more active, 

 the duration of the irritability is proportionally abbreviated; and the 

 muscles of Birds, whose respiration is peculiarly energetic, lose this 

 property at an earlier period after the cessation of the circulation, than 

 do those of Mammals. From experiments on the bodies of executed 

 criminals, who were previously in good health, Nysten ascertained that, 

 in the Human subject, the contractility of the several muscular struc- 

 tures, as tested by Galvanism, departs in the following time and order : 

 the left ventricle of the heart first ; the intestinal canal at the end of 

 45 or 55 minutes ; the urinary bladder nearly at the same time ; the 

 right ventricle after the lapse of an hour ; the oesophagus at the expira- 

 tion of an hour and a half; the iris a quarter of an hour later ; and lastly, 

 the ventricles of the heart, especially the right, which in one instance 

 contracted 16J hours after death. 



359. That the circulation of arterial or oxygenated blood through 

 the muscles, is the essential condition of the continuance of their irri- 

 tability, appears from this, that after the general death of the system, 

 and even after the removal of the brain and spinal cord, the muscles 

 will preserve their irritability, and the action of the heart itself will 

 continue for a long time, provided that the circulation be kept up 

 through the lungs by artificial respiration, on the principles hereafter 

 to be explained ( 688). But if, whilst the general circulation con- 

 tinues, the circulation through a particular muscular part be inter- 



