718 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



the level of the fluid in the capillary tube will remain almost constant, thus indi- 

 cating an absence of change in the bulk of muscle, for a decrease would, of course, 

 be indicated by a fall of fluid, and increase of bulk would raise the fluid in the 

 capillary tube. ■ By extremely accurate measurements a slight actual decrease in 

 volume may be made out. Thus, Valentine has determined that a muscle with a 

 volume of two thousand seven hundred and six cubic centimeters in contraction 

 in tetanus is reduced to two thousand seven hundred and four cubic centimeters, 

 while its specific gravity increases from 1061 to 1062. 



When a muscle is thrown into contraction, it does not occur sim- 

 ultaneouslj- in all the muscle-fibres. If a muscle-fibre be placed under a 

 microscope and then thrown into contraction a wave of undulation may 

 be seen to be rapidly propagated from one end of the fibre to the other. 

 This wave is especially sensible if the muscular fibre is fixed at each 

 extremity. If a long muscle, such as the sartorius of the frog, have 

 its motor nerve-filaments paralyzed by curare, and the muscle then 

 thrown into contraction by stimulating one extremity with an induction 

 current, the wave of contraction travels so slowly as almost to be 

 capable of being seen bj r the eye. If such a muscle be supported 



Fig. 284.— Curve illustrating the Propagation of the Wave of 

 Muscular Contraction. (Marey.) 



The lower of the two straight lines represents the point of the lever resting on the muscle nearest the 

 point of stimulation. If the time between the moment of commencing contraction at this spot and that of 

 commencing contraction at the spot on which the second lever rests be measured by counting the vibra- 

 tions of the tuning-fork, the rate of progression of the contraction may be determined. 



horizontally and two light levers be placed at a distance from each other 

 bearing on the muscle and writing over each other on a recording sur- 

 face (Pig. 283), if the muscle be then thrown into contraction by direct 

 stimulation the levers will not be elevated simultaneously, but a curve 

 similar to that represented in Pig. 284 will be produced. By measur- 

 ing the distance between the commencement of these two contractions 

 and knowing the rate of movement of the recording surface, the rate 

 of progression of the wave may be calculated. If, instead of stimulating 

 the muscle, the nerve (in such an experiment) be stimulated, if no curare 

 have been given both levers will be simultaneously elevated. 



According to Bernstein, the rate of progression in the muscles of 

 cold-blooded animals of the wave of contraction is about two to three 

 meters per second. " Its rate of progression is much more rapid in the 

 case of warm-blooded animals. 



