354 



GENERAL PHYSIOLOGY 



enormous quantity of energy, the reaction, is produced by an 

 excessively small quantity acting as the stimulus ; hence the one- 

 sided view of irritability as the capacity of responding to slight 

 stimuli with a disproportionately great evolution of energy. This 

 case, although representing a special condition, is very obvious 

 and wide-spread, and it is worth while to consider its details. 



If, as an irritable body, a muscle with its nerve be selected, and 

 as a stimulus the mechanical stimulus of pressure, the folloNving 

 arrangement can be made (Fig. 150). The calf-muscle (gas- 

 trocnemius) of a frog, the nerve of which (sciatic) has been freed, 



is suspended in a muscle- 

 holder, the thigh-bone to which 

 the muscle is attached at its 

 upper end being fastened by 

 a clamp. The lower end of 

 the muscle with the tendon of 

 Achilles is separated from the 

 bone, and in the tendon a slit 

 is made, into which a hook 

 attached to a long thread is 

 fastened. This thread is carried 

 over two easily moving wheels, 

 and, at its other end, is attached 

 to a pan containing a weight 

 of 100 gr. The nerve of 

 the muscle-preparation lies 

 stretched out upon a horizontal 

 stand. Every stimulation of 

 the nerve causes a twitch of 

 the muscle. If, now, a weight 

 of 10 gr. be allowed to fall upon 

 the nerve from a height of 

 about 1 cm., so that the nerve 

 is mechanically stimulated by 

 the pressure, at the moment 

 of stimulation a twitch of the 

 muscle occurs, and the muscle raises the weight of 100 gr. to 

 a height of about 1 cm. Here the quantity of energy that corre- 

 sponds to the work of the muscle is approximatelj- ten times 

 greater than the quantity of energy that has operated as a stimulus 

 upon the muscle ; and under favourable conditions the dispro- 

 portion can be even much greater. According to the law of the 

 conservation of energy it is clear that the considerable quantity of 

 energy that is set free externally in the reaction cannot be derived 

 by the transformation of the small quantity that has been intro- 

 duced into the organism in the stimulus. It must, therefore, have 

 come from the organism itself and must have been stored pre- 



FlG. 150. — Apparatus forthe demonstration of the 

 inequality of the stimulus and the reaction. 

 A nerve-muscle preparation is suspended upon 

 a myograph ; the muscle is loaded with a 

 weight of 100 gr. and its nerve is laid over a 

 glass plate supported by a stand. Upon the 

 nerve rests a small aluminium pan having a 

 sharp keel on the lower side, and into this a 

 weight of 10 gr. falls from a height of about 

 1 cm. At the moment of stimulation the 

 muscle contracts and raises the 100 gi\ about 

 1 cm. 



