CHEMICAL, PHYSICAL AND VITAL PROPERTIES. cxxix 



especially to the striped variety, but, so far as is known, it is essentially 

 the same in the non -striated tissue. 



The juice expressed from a muscle after death, and especially after rigidity has set 

 in, is acid, from the presence of lactic acid ; so that the cut surface of a dead muscle 

 reddens litmus-paper. On the other hand a perfectly fresh section of muscle in the 

 living body, or while it retains its irritability, is alkaline or neutral. But, while this 

 is true of a living muscle in its usual state, it gives a decided acid reaction after it 

 has been strongly exerted, as, for instance, after tetanic spasm excited by electricity 

 or by strychnia poisoning. The acid is probably generated by a change in the 

 saccharine matter of the muscle. Ultimately the tissue in all cases becomes alkaline 

 from putrefaction and the evolution of ammonia. 



Physical properties of muscle. A dead muscle has little strength, and may be 

 torn asunder by a force of no great amount. A living muscle readily yields to exten- 

 sion, and shrinks exactly to its original length when the extending force ceases. Its 

 elasticity is therefore said to be small in degree, but very perfect or complete in opera- 

 tion. A dead muscle, especially after cadaveric rigidity has come on, resists exten- 

 sion more powerfully, but does not afterwards return 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 known, but it differs greatly in degree in different 

 cases. It is usually paler in the involuntary 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 colour in different strata 

 of the same muscles. The redness is no doubt partly due to blood contained in the 

 vessels, but not entirely so, for a red colouring matter, apparently of the same nature 

 as that of the blood, is obviously incorporated with the fibres. 



Under 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 surface of 

 the muscle and the other a cross section made through its fibres, the needle will 

 deviate so as to indicate an electric current passing along the wire from the surface 

 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, but 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 phenomenon described is called " the 

 muscular current," and is supposed 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 degree of 

 sensibility, but its characteristic vital endowment, as already said, is irritability or 

 contractility, by which it serves as a moving agent in the animal body. 



Sensibility. This 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 

 direction of the limbs and other parts which are moved through means of the volun- 

 tary muscles, and we are thereby guided in directing 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 occurs the person cannnot 

 direct the movements of the affected limbs without the guidance of the eye. 



Irritability or Contractility. The merit of distinguishing this property of the 

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

 on the other, is due to Dr. Francis Glisson, a celebrated English physician of the 

 seventeenth century ; 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 comprehensive acceptation of the term has 



