THE STUDY OP MUSCLE PHYSIOLOGY. 189 



It is possible to see in these tracings a genetic relation, the 

 second figure being evidently derivable from the first, and the 

 third from the second, by the fusion of all the curves into one 

 straight line. 



The Muscle Tone. — There are a number of experimental facts 

 from which the conclusion has been drawn that tetanic contrac- 

 tion is accompanied by a muscle tone which is in itself evidence 

 of the nature of the contraction. 



We may safely conclude that, at all events, most of the mus- 

 cular contractions occurring within the living body are tetanic 

 — i. e., the muscle is in a condition of shortening, with only very 

 brief and slight phases of relaxation ; and that a comparatively 

 small number of individual contractions suffice for tetanus 

 when caused by the action of the central nervous system; 

 though, as proved by experiments on muscle removed from the 

 body, they may be enormously increased. While a few stimu- 

 lations per second suffice to cause tetanus, it will also persist 

 though thousands be employed. 



THE CHANGES IN A MUSCLE DURING CONTRACTION. 



Though the change in form is very great during the con- 

 traction of a muscle, the change in bulk is almost inappreci- 

 able, amounting to a diminution of not more than about jtsVti 

 of the volume. In fact, according to the latest investigator, 

 there is no diminution whatever. 



Since the fibers of striped muscle are of very limited length 

 (30 to 40 mm.), it would seem that a contraction originating in 

 one fiber must be capable of initiating a similar action in its 

 neighbor ; and, as the ends of the fibers lie in contact, it is easy 

 to understand how the wave of contraction spreads. Normally, 

 the contraction must pass from about the center of the muscle- 

 cell where the nerve terminates in the end-plate. 



THE ELASTICITY OP MUSCLE. 



In proportion as bodies tend to resume their original form 

 when altered by mechanical force are they elastic, and the ex- 

 tent to which they do this marks the limit of their elasticity. 



If a muscle (best one with bundles of fibers of about equal 

 length and parallel arrangement) be stretched by a weight 

 attached to one end, it will, on removal of the extending force, 



