MUSCULAR CONTRACTILITY. 135 



bility take place in chronic paralysis. There is a particular condition 

 or state of slight tension of healthy muscles, which, beyond their mere 

 elasticity, accounts for their retraction when they are cut across, and 

 which is named their tonicity, or tonic state. It is persistent only so 

 long as they are healthy, and remain in connection with the nerves 

 and nervous centres ; for if the nerves are cut, or if the nervous cen- 

 tres in connection with them are destroyed, the muscles lose their 

 tone and become flaccid. It is this property continually in action, 

 which serves, more than the elasticity already alluded to, to keep 

 antagonistic muscles in a due state of equilibrium, in varying positions 

 of the limb ; it seems also to be by a powerfully-exercised toriicity 

 that sphincter muscles, like that placed around the outlet of the ali- 

 mentary canal, are kept contracted. 



The muscular contractility is not extinguished immediately after 

 death, but is retained for different periods by different muscles, and 

 in different animals. For example, in the cold-blooded vertebrata, the 

 reptiles, frogs, and fishes, it may last for many hours, or even for 

 days ; a turtle's heart has been known to beat three days after the 

 death of the animal. In warm-blooded vertebrata, man, quadrupeds, 

 and birds, the irritability ceases a few hours after death, soonest of all 

 in birds. The irritability lasts longer in animals just born, and in 

 hibernating animals killed in the winter during their sleep. The 

 more active the respiration, the more active the muscular irritability ; 

 but the more dependent also is this irritability upon the respiratory 

 process, and hence its speedier extinction in animals the respiration 

 of which is active, and its longer duration in those the respiratory 

 changes of which are of a feebler character. In the human body the 

 irritability lasts longer in certain muscular parts than in others ; it 

 disappears first in the left ventricle of the heart, then, in succession, 

 in the intestines, stomach, urinary bladder, and right ventricle of the 

 heart, in all which parts it is lost before the expiration of an hour. 

 It afterwards expires in the voluntary muscles, first in the trunk, then 

 in the lower limbs, and lastly in the upper limbs. It continues still 

 later in the left auricle, and latest of all in the right auricle of the 

 heart, the ultimum morfens of Galen. It is totally lost within seven- 

 teen hours after death. The contractility is said to be destroyed, 

 sometimes immediately, in cases of death by lightning, or by violent 

 injuries to the nervous centres. It disappears only in cases of poison- 

 ing by carbonic acid gas or sulphuretted hydrogen. Cold air or water, 

 and narcotic agents, taken internally, are said to hasten its departure. 

 Narcotic solutions, morphia, cyanide and other salts of potassium, and 

 the upas poison injected into the blood, also lessen or destroy it, and 

 much more rapidly and effectively when directly applied to the mus- 

 cles, though not necessarily when applied only to the nerves. Im- 

 mersed in sulphurous acid, hydrogen, carbonic oxide, and carbonic 

 acid gases, the muscles lose their contractility partly or entirely. 

 Venous blood, which contains much carbonic acid, acts as a poison, 

 lessening their irritability ; whilst oxygen and arterial blood preserve 

 it, and the latter, defibrinated and injected into a limb recently dead, 



