244 



VETERINARY PHYSIOLOGY 



muscle, so far as its working power is concerned, an optimum 

 load. 



In studying tlie amount of work which a muscle, or set of 

 muscles can do, the element of time must always be considered. 

 Obviously, contracting muscles will do more work in an hour 

 than in a minute. 



Further, the rate at which the work is done has an 

 important influence, and the amount of work which can 

 be done per unit of time will depend not merely on the 

 condition of the muscle and the load, but upon the rate at 



Lift 



Work output 



4'7 kgm. 



per unit of time. 



Strong stimuli. 



L«t I I I I I I I I I I I I I 



Work output 



6 kgm. 



per unit of time. 



Weaker stimuli. 



Fig. 126. — To show the influence of varying the strength of stimulation 

 on the work done per unit of time. 



which the lifting is performed. This will depend upon 

 (1) the strength of the stimuli and (2) the rate of stimula- 

 tion. 



(1) Increasing the rate of work by the apjilication of a 

 very strong stimulus at short intervals may rapidly lead to 

 fatigue, and thus to a comparatively low output of work in 

 the time of the experiment, while a smaller stimulus at the 

 same rate mav cause a much longer continuance of the 

 response of the muscle and an actually greater output in 

 the total time (fig. 126). 



(2) On the other hand, a stimulus too rapidly applied may 

 soon lead to fatigue, while if more slowly applied the onset 

 of fatigue may be postponed and the work done in- 

 creased (fig. 127). 



The same is seen when the work of muscles in bulk is 

 studied. Experiments by Zuntz showed that in the horse, 



