GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 



77 



work, the contraction is recorded in the form of a curve, the width of 

 the arms of which will depend on the rate of movement. The time 

 relations of the phases of the contraction can be obtained by placing 

 beneath the lever a pen attached to an electro-magnet thrown into 

 action by a turning-fork vibrating in hundredths of a second. In 

 order to determine the rapidity with which the contraction follows 

 the stimulation, it is essential that the moment of the latter be also 

 recorded. This is accomplished by an automatic key, the opening 

 or closing of which develops the stimulus which excites the muscle. 

 A combination of these different appliances constitutes a myograph 

 and the curve of contraction a myogram. (See Fig. 23.) 



The Isotonic Myogram. With the object of obtaining a curve 

 of successive changes in the length of a muscle during a single con- 

 traction and at the same time avoiding changes in tension, the weight 



FIG. 24. THE ISOTONIC MYOGRAM. 



attached to the lever should be applied close to its axis, a mechanic 

 condition which practically maintains a uniform tension throughout 

 the contraction. To this method the term "isotonic" has been given 

 and the curve so obtained an isotonic myogram.* 



The Character of an Isotonic Myogram. With the muscle 

 arranged as previously described and stimulated directly with a single 

 induction shock, the contraction will be recorded in the form of a 

 curve similar to that represented in Fig. 24, in which the line 1 1 repre- 

 sents the abscissa of time; a, the moment of stimulation; and bed, 

 the degree of shortening at each successive moment. The undulating 

 line shows the time relations, the distance from crest to crest represent- 



* In the ordinary method of recording a muscular movement, i. e. y with the weight 

 attached to the lever immediately beneath the muscle and known as the "loaded 

 method," a certain momentum is imparted to the weight, which continues after the 

 muscle has ceased to act, both when shortening and relaxing, and so imparts to the re- 

 cording lever additional movements which vitiate the true character of the curve. 



