124 MUSCULAR TISSUE. 



stimulus may be either directly applied to tlae nerve of the muscle, as when that 

 nerve is itself mechanically irritated or galvanised : or it may l^e first made to 

 act on certain other nerves, by which its influence is. so to speak, conducted in 

 the first instance to the brain or si:)inal cord, and then transferred or reflected to 

 the muscular nerve. 



The stimuli to which muscles are obedient are of various kinds ; those best 

 ascertained are the following, viz. : 1. Mechanical irritation of almost any sort, 

 under which head is to be included sudden extension of the muscular fibres. 

 2. Chemical stimuli, as by the application of salt or acrid substances. ?>. Elec- 

 trical ; usually by means of a galvanic current made to jjass through the muscular 

 fibres or along the nerve, -t. Sudden heat or cold ; these four may be classed 

 together as /^////.v/rc/Z .stimiiU. Next, menial xtiiiiHli, viz : 1. The operation of the 

 will, or volition. 2. Emotions, and some other involuntary states of the mind. 

 Lastly, there still remain exciting causes of muscular motions in the economy, 

 which, although they may probably tiu'n out to be physical, are as yet of doubt- 

 ful nature, and these until better known may jierhaps without impropriety be 

 called orffdiiir .^fiimili ; to this head may be also referred, at least provisionally, 

 some of the stimuli which excite convulsions and other mvoluntary motions 

 which occur in disease. 



Duration of irritability after death. — It is known that, if the supply of nu- 

 trient material be cut off from a muscle by arresting the flow of blood into it, its 

 contractility will be impaired, and soon extinguished altogether, but will after a 

 time be recovered again if the supply of blood be restored. The influence of the 

 blood supplied to muscles in maintaining their contractility lias l^een strikingly 

 showTi by Brown-Sequard, who has succeeded in restoring muscular contractility 

 in the bodies both of man and animals some time after death, and after it had 

 become to all appearance extinct, by injecting into the vessels arterial blood 

 iiejirived of its flbrin, or deflbrinated venous blood i^reviously reddened by expo- 

 «iu'e to the air. In warm-blooded animals in which the nutritive process is more 

 active, and the expenditure of force more rapid, the maintenance of irritability 

 is more closely deiDendent on the supply of blood and the influence of oxygen, so 

 that it sooner fails after these are cut off. In accordance with this statement, 

 it is known that while the muscles of man and qiiadrujieds cease to be irritable 

 within a few hours after death, and those of birds still sooner, the muscular 

 irritability will remain in many reptiles and fishes, even for days after the 

 extinction of sensation and volition and the final cessation of the respiration and 

 circialation — that is, after systemic death. A difference of the same kind is 

 observed among warm-blooded animals in different conditions ; thus irritability 

 endures longer in new-born animals than in those which have enjoyed respira- 

 tion for some time and are more dependent on that fiinction ; and, in like 

 manner, it is very lasting in hybemating animals killed during their Avinter 

 sleep. 



But the duration of this property differs also in different muscles of the same 

 animal. From numerous careful observations Nysten concluded that in the 

 human body its extinction takes place in the following order, viz. : 1 , the left 

 ventricle of the heart ; 2, the intestines and stomach : 3, the urinary bladder ; 

 4, the right ventricle ; in these generally within an hour ; '>, the gullet : (!, the 

 iris ; 7, the voluntary muscles, a, of the trunk, b. of the lower and e. of the upper 

 extremities ; 8, the left aiu-icle. and, 9, the right auricle of the heart, which last 

 was on this account styled by Galen the " ultimum moriens." In one case Xysten 

 observed the right auricle to continue irritable for sixteen houi-s and a half after 

 death. But it has been recently found that a voluntary muscle may give .signs 

 of a certain degree of irritability even later than this, if it be struck a smart 

 blow with a blunt edge, such as the back of a knife, across the du-ection of the 

 fibres. The contraction then produced is quite local, and confined to the parts 

 struck. Funke states that he and the brothers ^^'eber obtained this result in the 

 body of a decapitated criminal twenty-four hours after death. 



The time of duration is affected by the mode of death. Thus the irritability is 

 said to be almost wholly and immediately extinguished Tjy a fatal stroke of 

 lightning, and to disappear very speedily in the bodies of persons stifled by 

 noxious vapours, such as carbonic acid, and especially sulphuretted hydrogen. 



