48 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



of recording with levers (von Kries) or by the newer method of 

 photographing the electrical oscillations shows, on the contrary, 

 that even the shortest possible voluntary contractions are brief 

 tetani made up of a short lasting series of contractions fused 

 together. In all probability, therefore, our motor centers, when- 

 ever they are stimulated by a so-called act of the will, discharge 

 rhythmically a series of nerve impulses. As we shall see later, 

 it is possible that certain of these centers, when stimulated 

 reflexly, may discharge a single nerve impulse and thus arouse 

 a simple muscular contraction (see Knee- kick). 



The Ergograph. Voluntary contractions in man may be re- 

 corded in a great many ways, but Mosso has devised a special in- 

 strument for this purpose, known as the ergograph. It has been 

 much used in quantitative investigations upon muscular work 

 and the conditions influencing it. The apparatus is shown and 

 described in Fig. 23. The person experimented upon makes a 

 series of short contractions of the flexor muscle of the middle 

 finger, thereby lifting a known weight to a definite height 

 which is recorded upon a drum. In a set of experiments the 

 rate of the series of contractions that is, the interval of rest 

 between the contractions is kept constant, as also is the load lifted. 

 Under these conditions the contractions become less and less exten- 

 sive as fatigue comes on, and finally, with the strongest voluntary 

 effort, the contraction of the muscles is insufficient to lift the weight. 

 In this way a record is obtained such as is shown in Fig. 24. In 

 such a record we can easily calculate the total work done by 

 obtaining the product of the load into the lift for each contrac- 

 tion and adding these products together. By this means the 

 capacity for work of the muscle used can be studied objectively 

 under varying conditions, and many suggestive results have been 

 obtained, some of which will be referred to specifically.* It should 

 be borne in mind, however, that the ergograph in this form does 

 not enable us to compute the total work that^the muscle is capable 

 of performing. It is obvious that when the point of complete 

 fatigue is reached, as illustrated in the record, Fig. 24, the muscle is 

 still capable of doing work, that is external work, if we replace the 

 heavy 'load by a lighter one. For this reason some investigators 

 have substituted a spring in place of the load,f giving thus a 

 spring ergograph instead of a weight ergograph. Although with the 

 spring ergograph every muscular contraction is recorded and the 

 entire work done may be calculated, it also possesses certain theo- 



* Mosso, "Archives italiennes de biologie," 13, 187, 189; also Maggiora, 

 1890, p. 191, 342. Lombard, "Journal of Physiology," 13, 1, 1892. 



t Franz, "American Journal of Physiology," 4, 348, 1900; also Hough, 

 ibid., 5, 240, 1901. 



