VITAL rilOPEETIES OF MUSCLE. 123 



ceases. Its elasticity is therefore said to be small in degree, but very perfect or 

 complete in operation. A dead muscle, especially after cadaveric rigidity has 

 come on. resists extension more powerfully, but does not afterwards retiuii to its 

 original length ; hence its elasticity is said to be greater than that of the living- 

 muscle, but less perfect. 



The red colour of muscle is well kno-^-n, but it differs gi-eatly in degree in 

 different cases. It is usually paler in the invohxntary muscles ; but here the 

 heart again is a striking exception. In most fish the chief muscles of the body 

 are nearly colourless, and in the breast of wild fowl we see a difference in the 

 depth of coloru" in different strata of the same muscles. The redness is no doubt 

 partly due to blood contamed in the vessels, but not entirely so, for a red colour- 

 ing matter, apparently of the same natvu-e as that of the blood, is obviously 

 incorporated with the fibres. 



Lender this head must also be mentioned the manifestation of electricity by a 

 quiescent but living muscle. "When a muscle taken from a living or recently 

 killed animal (a frog is commonly used) is brought into connection with the 

 ends of a very delicate galvanometer, so that one extremity of the latter touches 

 the outer siu-face of the muscle and the other a cross section made through its 

 fibres, the needle will deviate so as to indicate an electiic cuiTent passing along 

 the wire from the siuface of the muscle to its cross section. If both ends of the 

 galvanometer touch points in the length of the muscle equidistant from its 

 middle, no effect ensues, bvit if one point of contact be farther than the other 

 from the middle, a current will pass along the wire from the nearer to the more 

 distant point. The same results are obtained with a small shred or fasciculus 

 of the muscle. The i:)henomenon descri1)ed is called " the muscular ciu-rent," and 

 is sui^iiosed to indicate a state of electric polarity in the particles of the muscle, 

 probably caused by chemical changes going on in its substance. 



Vital properties of muscle. — The muscular tissue possesses a considerable de- 

 gree of fien.sihtUt)/. but its characteristic vital endo'mnent, as already said, is 

 ■irritahUitij or rant racti lit//, by which it serves as a moving agent in the animal 

 l)ody. 



tScns third)/. — Tliis property is manifested by the pain which is felt when a 

 muscle is cut, lacerated, or otherwise violently injured, or when it is seized with 

 spasm. Here, as in other instances, the sensibility belongs, properly speaking, to 

 the nerves which are distributed through the tissue, and accordingly, when the 

 nerves going to a muscle are cut. it forthwith becomes insensible. It is by means 

 of this property-, which is sometimes called the " muscular sense." that we become 

 conscious of the existing state of the muscles which are subject to the will, or 

 rather of the position and dhection of the limlis and other parts which are moved 

 through means of the voluntary muscles, and we are thereby guided in du-ecting 

 our voluntary movements towards the end in view. Accordingly, when this 

 muscular sense is lost, while the power of motion remains, — a case which, though 

 rare, yet sometimes occiu's — the i^erson cannot direct the movements of the 

 affected limbs without the guidance of the eye. 



IrrUahUifij or Contrnrfiliftj. — The merit of distinguishing this property of the 

 animal body from sensibility on the one hand, and from mere mechanical pheno- 

 mena on the other, is due to Francis Giisson, a celebrated English physician 

 of the seventeenth centuiy ; but irritability, according to the view which he 

 took of it, was supposed to give rise to various other phenomena in the animal 

 economy besides the visible contraction of muscle, and his comj^rehensive accep- 

 tation of the tenn has been adopted by many succeeding authorities, especially 

 by writers on pathology. Haller in his use of the term initabihty, restricted it 

 to the peculiar property of muscle. 



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

 stimuliis. The stimidus may be applied immediately to the muscular tissue, as 

 when the fibres are irritated with a sharp point : or it may be apjjlied 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 '' v-is nervosa." 

 is distinguished from contractility, which is confined to the muscle. Again, a 



