24 PHYSIOLOGY OF MUSCLES AND NERVES. 



former also exhibit another peculiarity. If a weight ig 

 attached to a steel wire, or some other similar body, 

 the latter extends, and retains its new length so long 

 as the weight acts upon it ; but as soon as the weight 

 is removed the steel resumes its original length. It is 

 not so in the case of inorganic bodies. For instance, 

 if a weight is attached to a caoutchouc thread it will be 

 found that the latter is immediately extended to a 

 certain length ; but if the weight is not removed, it 

 will be found that the caoutchouc thread extends yet 

 more, and the weight continues to sink, though, indeed, 

 but slowly, and, as time goes on, with ever decreasing 

 speed. But even at the end of twenty-four hours a 

 slight additional extension of the thread is observable. 

 If the weight is then removed, the thread immediately 

 becomes considerably shorter, but does not entirely re- 

 vert to its original length ; it attains the latter very 

 gradually and in the course of many hours. This phe- 

 nomenon is known as the gradual extension of organic 

 bodies. It takes place in very considerable degree in 

 muscle, and natm*ally increases the difficulty of deter- 

 mining the extensibility of muscles, in that the mea- 

 surements differ according to the moment at which they 

 are read. It is safest to take into consideration only 

 that extension which occurs instantaneously, without 

 regard to that which gradually follows. 



Various apparatus have been produced for examina- 

 tion of muscular extension. The latter can be most 

 accuratel}' read by means of the apparatus invented by 

 du Bois-Reymond, represented in fig. 7. The muscle 

 is firmly fastened to a fixed bearer, its upper tendon 

 being fixed in a vice. A small, finely graduated rod is 

 fastened to the lower tendon by means of a small hook. 



