Muscular Tissue 41 



ence of fatigue. In the body the circulation of blood both brings fresh 

 food material, to be built up into new muscle material, and also removes 

 the waste products. If the muscle activity is relatively great, however, 

 the waste product cannot be removed as fast as formed, and either the 

 food material is not brought fast enough, or else the muscle cell cannot 

 fast enough build up muscle material out of it. 



THE ELECTRICAL PROPERTIES OF MUSCLE. 



Under certain conditions an electric current may be drawn off from a 

 muscle by applying suitable electrodes to it. If one electrode (A) is ap- 

 plied to an uninjured portion of a resting muscle, and the other (B) to a 

 cut or otherwise injured portion, a delicate galvanometer in circuit with A 

 and B will show a very small current flowing from A to B. This is spoken 

 of as the ' current of demarcation ' or ' resting current '. 



If electrodes are applied to an uninjured muscle at some distance from 

 each other, and the muscle is caused to contract, a current flows during 

 contraction from the electrode at which the degree of contraction is lowest 

 to the electrode at which it is highest. If, therefore, the muscle be stimu- 

 lated at a point M, near one end, the electrode A being applied at the 

 middle of the muscle and the electrode B at the other end, when the exci- 

 tation wave reaches A, the current will flow from B to A, and when the 

 wave reaches B, the current will flow in the reverse direction. This cur- 

 rent is known as the ' current of action ' or ' action current '. 



The currents for muscle may not be of any special significance. They 

 are in any case probably artifactual, that is, there is probably no current 

 unless electrodes are applied and an external circuit established through 

 them. In the case of the ' resting current ' there may not even be a differ- 

 ence of potential betwen the cut and uninjured portions before the elec- 

 trodes are applied. 



REFERENCES ON MUSCLES. 



Bailey, Histology, Pt. Ill, Chapter V. 



Lewis & Stohr, Histology, Pt. I, § II, Sub-§ Muscular Tissue. 



Shafer, Microscopic Anatomy, § Structure of the Tissues, Sub-§ Muscular Tissue. 



Sanderson, J. B., The Mechanical, Thermal, and Electrical Properties of Striped 



Muscles. Schafer's Text-Book of Physiology. 

 Howell, A Text-Book of Physiology, Chapters I & II. 

 Starling, Physiology, Chapter V. 

 Luciani, Human Physiology, (Translated by Welby), Vol. I, Chapter IX. Vol. Ill, 



Chapter I. 



