FUNCTIONS OF MUSCULAR TISSUE. 331 



nervous influence, as when subjected to it; and being, like Irritability, an inher- 

 ent property of the tissue itself, the presence of which is characteristic of its 

 living state. It manifests itself in the retraction which takes place in the ends of 

 a living muscle, when it is divided (as is seen in amputation) ; this retraction 

 being permanent, and greater than that of a dead muscle. But its effects are 

 much more remarkable in the non-striated, than in the striated form of Muscu- 

 lar fibre ; and are particularly evident in the contractile coat of the Arteries, 

 causing the almost entire obliteration of their tubes, when they are no longer 

 distended with blood. The disposition to tonic contraction is increased by any 

 considerable change of temperature; the power of Heat is well seen in the follow- 

 ing experiments by John Hunter : " As soon as the skin could be removed from 

 a sheep that was newly killed, a square piece of muscle was cut off, which was 

 afterwards divided into three pieces, in the direction of the fibres ; each piece 

 was put into a basin of water, the water in each basin being of different tem- 

 peratures, viz., one about 125, about 27 warmer than the animal ; another 

 98, the heat of the animal; and the third 55, about 43 colder than the ani- 

 mal. The muscle in the water heated to 125 contracted directly, so as to be 

 half an inch shorter than the other two, and was hard and stiff. The muscle 

 in the water heated to 98 after six minutes began to contract and grow stiff; 

 and at the end of twenty minutes it was nearly, though not quite, as short and 

 hard as the above. The muscle in the water heated to 55, after fifteen minutes, 

 began to shorten and grow hard; after twenty minutes it was nearly as short and 

 as hard as that in the water heated to 98. At the end of twenty-four hours, 

 they were all found to be of the same length and stiffness." 1 The agency of 

 Heat in producing this contraction is also remarkably shown in the fact, that if 

 a Frog be immersed in water of the temperature of 110, the muscles of its 

 body and limbs will be thrown into a state of permanent and rigid contraction. 

 But it would seem that these effects are chiefly, if not entirely, exerted upon 

 the striated form of Muscular fibre ; and that the tonicity of the non-striated fibre 

 is called into play by Cold, rather than by heat. For if a Tadpole or Frog be 

 immersed in water, the temperature of which is gradually raised, until this state 

 of contraction comes on, the Heart will be found to continue pulsating for many 

 hours afterwards, not being affected by the heat. On the other hand, if an 

 artery in a living warm-blooded animal be exposed to cold air for some time, the 

 lowering of its temperature occasions its contraction to such an extent, that its 

 cavity becomes almost obliterated. The influence of warmth in diminishing, 

 and of cold in increasing, the tonic contraction of the Arterial system, will be 

 'adverted to hereafter (CHAP. ix. SECT. 3). 



332. The distinctness of the Tonicity of Muscles from their Irritability, is 

 further shown by the fact, that the former commonly survives the latter; and 

 that it is not destroyed by treatment which occasions the complete departure of 

 the Irritability. The first of these statements finds its proof in the phenomena 

 of " cadaveric rigidity" to be presently adverted to. Of the latter, the follow- 

 ing remarkable experiment by John Hunter is an ample demonstration : " From 

 a straight muscle in a bullock's neck, a portion, three inches in length, was 

 taken out immediately after the animal had been knocked down, and was ex- 

 posed between two pieces of lead, to a cold below 0, for fourteen minutes ; at 

 the end of this time it was found to be frozen exceedingly hard, was become 

 white, and was now only two inches long : it was thawed gradually, and in about 

 six hours after thawing it contracted so as only to measure one inch in length ; 

 but irritation did not produce any sensible motion in the fibres. Here, then, 

 were the juices of muscles frozen, so as to prevent all power of contraction in 



1 " General Principles of the Blood," in " Hunter's Works," (Palmer's Edition,) vol. iii. 

 p. 110. 



