COMPOUND TUBULAR TISSUES. 37 



which is meant, the power oftnovmg responsive to irritation. It is 

 not the mere mechanical power by which elastic substances shorten 

 themselves on the removal of a distending force, but it is an endow- 

 ment responsive to appropriate stimuli, and diminishing or disap- 

 pearing with the healthy state of the tissue. Elasticity is a mere 

 physical property. Contractility is a vital property. 



Whatever is capable of inducing contraction in muscles, when 

 applied to them, is called a stimulus. Chemical agents, mechanical 

 applications, and irritating substances are included under this head. 

 In the living body the ordinary stimulus exciting contraction is the 

 nervous influence. Muscular contraction, however, is not dependent 

 on this influence, since it can be excited after all connexion with the 

 nervous centres has been destroyed, and even in a single isolated 

 fibrilla. 



The contractility of a muscle may be exhausted by repeated exer- 

 cise, as well as by the continued application of any of the above 

 stimuli, but it may be recovered again, provided sufficient interval 

 of rest be afforded to it. " In regarding contractility, therefore, as a 

 property of living muscular fibre in general^ it is meant that it resides 

 in it as a property, without which it would not be muscle ; and in 

 such a manner, that no particle, however microscopic, can be de- 

 tached from a muscle which does not of itself, and independently of 

 the rest, possess this property as long as it possesses vitality." 



Muscles are abundantly supplied with blood-vessels and nerves. 

 The capillary vessels ramify in the spaces between the fibres, but 

 never penetrate the sarcolemma, the nutritive materials being proba- 

 bly supplied by the selecting power of cells. The nerves are WLOtor 

 nerves^ and they are exceedingly abundant, terminating in the sub- 

 stance of the muscle in loops. The muscles of organic life are but 

 little influenced by nervous power, but depend for their stimulation 

 upon the presence of substances brought immediately ipto contact 

 with them. The muscles therefore have but little sensibility. 



Every fibre of the striated muscles is attached by its extremities 

 to white fibrous tissue ; through the medium of which it exerts its 

 contractile power on the bone, or other substance to be moved : the 

 union of all these white fibres constitutes the tendon. The muscular 

 fibre ends by a perfect disc, and with the whole surface of this disc 

 the tendon is connected and continuous, with it and the sarcolemma. 



Muscular contraction is accompanied by the production of sound 

 and heai^ both of which are probably produced by the movements of 

 the neighbouring fibres upon each other. The heat may also be 

 produced by the chemical changes resulting from the disintegration 

 of the muscular tissue consequent upon its use. This elevation of 

 temperature is sometimes as high as 2° Fahr. 



The rigor mo?-tis, or the stiffening of the body after death, is due 

 to the contraction of the muscles, and, like the coagulation of the 

 blood, is the last act of their vitality. Where the individual has died 

 of a wasting disease, if comes on early, and lasts but a short time, 



4 ■ 



