cxxx MUSCULAR TISSUE. 



been adopted by many succeeding authorities, especially by writers on pathology. 

 Haller, in his use of the term irritability, restricted it to the peculiar property of 

 muscle. 



Stimuli. In order to cause contraction, the muscle must be excited by a stimulus. 

 The stimulus may be applied immediately to the muscular tissue, as when the fibres 

 are irritated with a sharp point ; or it may be applied to the nerve or nerves which 

 belong to the muscle : in the former case, the stimulus is said to be " immediate," in 

 the latter, "remote." The nerve does not contract, but it has the property, when 

 stimulated, of exciting contractions in the muscular fibres to which it is distributed; 

 and this property, named the " vis nervosa," is distinguished from contractility, 

 which is confined to the muscle. Again, a stimulus maybe either directly applied to 

 the nerve of the muscle, as when that nerve is itself mechanically irritated or galva- 

 nised ; or it may be 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 spinal cord, and then 

 transferred or reflected to the muscular nerve. 



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

 tained 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. 3. Electrical ; usually by 

 means of a galvanic current made to pass through the muscular fibres or along the 

 nerve. 4. Sudden heat or cold ; these four may be classed together as jthysical 

 stimuli. Next, mental stimuli, 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 pro- 

 bably turn out to be physical, are as yet of doubtful nature, and these until better 

 known may perhaps without impropriety be called organic stimuli; to this head 

 may be also referred, at least provisionally, some of the stimuli which excite convul- 

 sions and other involuntary motions which occur in disease. 



Duration of irritability after death. It is known that, if the supply of nutrient 

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

 tility 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 sup- 

 plied to muscles in maintaining their contractility has been strikingly shown by Dr. 

 Brown-S6quard, 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 ap- 

 pearance extinct, by injecting into the vessels arterial blood deprived of its fibrin, 

 or defibrinated venous blood previously reddened by exposure 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 dependent 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 quadrupeds 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 circulationthat 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 

 respiration for some time and are more dependent on that function; and, in 

 like manner, it is very lasting in hybernating animals killed during their winter 

 sleep. 



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

 animal. From numerous careful observations Uysten 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; 5, the gullet; 6, the iris; 7, the 

 voluntary muscles, a, of the trunk, 6, of the lower and c, the upper extremities ; 

 8, the left auricle, and, 9, the right auricle of the heart, which last was on this 

 account styled by Galen the " ultimum moriens." In one case Nysten observed the 

 right auricle to continue irritable for sixteen hours and a half after death. But it has 

 been recently found that a voluntary muscle will give signs of a certain degree of 



