318 OF THE PRIMARY TISSUES OF THE HUMAN BODY. 



tact of a solid substance, especially if it be pointed ; thus we may excite con- 

 tractions in Muscular fibres, by simply touching them with the point of a needle 

 or of a scalpel. Most substances of strong chemical action, such as acids and 

 alkalies, will excite the fibres to contraction, when directly applied to themselves; 

 but the most powerful agent of all is Electricity. If we irritate mechanically 

 a portion of a muscle composed of striated fibre, the biceps, for example, the 

 fasciculus of fibres which is touched will immediately contract, and that one 

 only ; and the contracted fasciculus will soon relax, without communicating its 

 movements to any other. The Heart, however, exhibits a different action, which 

 is probably dependent upon the peculiar arrangement of its fibres, whereby the 

 contraction of one set gives a mechanical stimulation to others ; for the muscular 

 substance of a large part of the organ is thrown into rapid and energetic con- 

 traction, by a stimulus applied at any one point ; and this contraction is speedily 

 followed by relaxation, which is again succeeded by a number of alternating 

 contractions and relaxations. On the other hand, if we apply a similar irrita- 

 tion to a portion of non-striated fibre, as that of the Intestinal canal, the fasci- 

 culus which is stimulated will contract less suddenly, but ultimately to a greater 

 amount; its relaxation will be less speedy; and, before it takes place, other 

 fasciculi in the neighborhood begin to contract ; their contraction propagates 

 itself to others; and so on. In this manner, successive contractions and relaxa- 

 tions may be produced through a considerable part of the canal, by a single 

 prick with a scalpel ; a sort of wave of contraction being transmitted in the 

 direction of its length, and being followed by relaxation. Again, in the Mus- 

 cular structure of the Bladder and Uterus (when the latter is fully developed), 

 direct irritation excites immediate and powerful contractions, which extend 

 beyond the fasciculus actually irritated, and produce a great degree of shorten- 

 ing ; but they do not alternate, in the healthy state, with any rapid and decided 

 elongation. And in the muscular tissue of the middle coat of the Arteries, the 

 contraction takes place nearly in the same manner ; a considerable degree of 

 shortening being effected by the contraction of other fasciculi than those directly 

 irritated, and this shortening not giving way speedily to relaxation ; but a pro- 

 longed application of the stimulus is often necessary to produce the effect. 

 The effects of Electrical stimulation applied to the Muscles themselves, are very 

 similar ; but it is more difficult to confine the irritation to particular fasciculi of 

 a voluntary muscle, and more easy to throw the whole mass into contraction at 

 once by the transmission of a slight charge through it ; and on certain forms 

 of the non-striated fibre, the electric stimulus produces effects more decided than 

 can be evoked in any other way. The difference in the endowments of the two 

 kinds of tissue is particularly well seen, when they are subjected to the magneto- 

 galvanic apparatus, which transmits a rapid succession of slight electric shocks ; 

 for these, in the striated muscles, immediately excite a state of rigid contraction 

 which lasts as long as the stimulus is transmitted, but ceases immediately that 

 it is withdrawn ; whilst in the non-striated fibres, the contraction is slowly ex- 

 cited, sometimes alternates with rest, and continues for a time after the electric 

 discharges have ceased. Of this form of contractility, the muscular coats of 

 the smaller arteries afford a particularly good example ; for they may be made 

 to contract by the magneto-galvanic apparatus, until they become quite imper- 

 vious to blood ; and yet the contraction neither takes place immediately upon 

 the application of the stimulus, nor does it give place to relaxation directly that 

 it is intermitted. 1 



317. On the other hand, when the stimuli which excite Muscular Contractility 

 are applied to the nerves which supply any muscle composed of striated fibre (the 



1 See Prof. Weber's researches upon this subject, in Wagner's " Ilandworterbuch der 

 Physiologic," Art. "Muskelbewegung;" and " Mailer's Archiv.," 1847, band ii. 



