58 



PRACTICAL PHYSIOLOGY 





The effect of load, and of its method of application on a single 

 muscular contraction, will be studied in the following ways : (a) the 

 contraction given by a muscle loaded and after-loaded with the same 



weight will be compared; (b) a con- 

 stant load will be thrown on to a 

 muscle as an after-load later and later 

 in its period of shortening, and the 

 effect on the contractions noted ; (c) the 

 muscle being just completely after- 

 loaded, the height of contraction, 

 with increasing loads, will be mea- 

 sured and the work done with each 

 calculated. 



Comparison of the Contractions of 

 a Loaded and After-loaded Muscle. 

 Arrange the apparatus for stimulating 

 IJj a muscle with single maximal induc- 

 |~ tion shocks, using the drum as a key 

 2"! in the primary circuit. Fix a gastro- 

 j| cnemius preparation to a myograph 

 gg lever, provided with an after-loading 

 j > screw ; by raising the screw the metal 

 g* part of the lever can be supported at 

 |? any level (Fig. 25). Hang a weight 

 J "! of 50 grms. near the axis and raise the 

 J | screw until the whole of the weight 

 | is just after-loaded ; this point can be 

 5 ascertained by supporting the weight 

 I with the finger, and when the muscle 

 | no longer tends to raise the lever off 

 o the after-loading screw, the muscle is 

 J unstretched by any load. Arrange the 

 | apparatus so that with the screw in 

 | this position the lever is horizontal. 

 jj Record a single contraction of the 

 o- muscle on a rapidly revolving drum, 

 mark the point of stimulation, and 

 draw an abscissa. Then lower the 

 after-loading screw until the muscle is 

 loaded with the whole weight, and super-impose on the same abscissa 

 and with the same point of stimulation a contraction of the loaded 

 muscle (Fig. 58). 



