6 PHYSIOLOGY CHAP. 



venous stream by each contraction of the muscles. But in curar- 

 ised animals also direct excitation of the muscles dilates the 

 vessels and may produce minute capillary extravasations owing to 

 excess of tension. 



The nutrition of the muscles, and indirectly their excitability, 

 also depend on the trophic influence continually exercised upon 

 them by the nervous system. After cutting the motor nerves the 

 muscles degenerate as well as the peripheral end of the nerves 

 severed from their centre. Their excitability falls in the first three 

 or four days, but then rises to mechanical and galvanic excitation 

 (Erb's reaction of degeneration), while it decreases still further to 

 faradic stimulation; after seven weeks muscular excitability is much 

 reduced, and within six to seven months it has disappeared. During 

 the first week after section fibrillary contractions are observed in 

 the degenerating muscle, which are due to the excitation of the 

 contractile elements by intrinsic chemical changes (Schiff). 



Use and disuse again have great influence upon the nutrition, 

 and thus upon the excitability and work-capacity, of muscle. It 

 is a common observation that exercise develops and strengthens 

 the muscles, while disuse and a sedentary life render them weak 

 and flabby. Absolute enforced rest causes the muscles in time to 

 degenerate and atrophy. 



II. The physiology of muscle was not really known till after 

 the ingenious researches of E. Weber (1846) on the relations 

 between contractility and elasticity; and till Helmholtz (1850-52) 

 applied the graphic method to its study by means of his myograpli, 

 which traces the entire curve of a muscular contraction (myogram) 

 and indicates the exact moment of the application of the stimulus 

 to the nerve or to the muscle. 



A Myograpli is an apparatus designed to show by a tracing on a smoked 

 plate or revolving cylinder the changes in length (or thickness) which a 

 muscle, undergoes during excitation, i.e. the active state into which it is 

 thrown as the effect of stimulation. 



There are a great variety of these instruments, invented by the different 

 authors who have occupied themselves with the mechanical functions of the 

 muscles. One of the oldest is that of Pfliiger, which again is only a simpli- 

 fication of the original myograpli devised by Helmholtz. Pfliiger's apparatus 

 (Fig. 1) consists of an arm LL which moves round a horizontal axis, and can 

 be brought into equilibrium by the counterpoise C. The other end of the arm 

 is fitted with a lever, which also rotates round an axis and ends in a metal 

 point P, which writes on a moving smoked plate or drum that can be rotated 

 at varying speeds. The writing-point is kept in contact with the recording 

 surface by a small weight or spring, but can be drawn back by a thread 

 fastened to the wheel c. A freshly excised muscle is clamped at the top, and 

 attached below by a thread and hook to the middle of the lever. Below the 

 point at which the muscle is attached is a small scale-p^i B, on which different 

 weights can be placed to examine the influence of different loading on the 

 contractility of the muscle. The latter is kept moist in a glass chamber con- 

 taining a little wet filter paper. 



Instruments of this class give an imperfect record because the myograms 



