ELECTRO-PHYSIOLOGY. 



587 



ing-screws,, and their lower extremities dip into the groove filled with 

 a saturated solution of sulphate of zinc. The arched plates are called 

 the bridge. Three Daniell cells are connected to the binding-screws, 

 with the interposition of a key. The binding-screws are united to 

 electrodes upon which lie the nerve-muscle preparation. When the 

 key is closed the muscle contracts and in the interval relaxes, except 

 when there is a rotation of the bridge. 



Then suddenly rotate the handle with its two zinc arms. This 

 is equivalent to a sudden variation of the intensity of the current, 

 the current, of course, continuing to pass all the time. The muscle 

 suddenly contracts. The response of a muscle or nerve to electrical 



Fig. 222. The Nerve-muscle Preparation. (STIRLING.) 



S, The nerve-muscle. F, Lower third of femur. /, Tendon of 

 gastrocnemius muscle. 



stimulation is due not to the simple flow or intensity of a current 

 through the tissues, but rather to the more or less sudden change in 

 the strength of the current. Sudden increase or decrease may act 

 as an efficient stimulus, but the gradual increase or decrease of the 

 current causes no response (Du Bois's law.) 



Differential Rheotome. The rheotome of 'Bernstein is an instru- 



lent by which a series of stimuli can be led into a nerve or muscle, 

 md the consequent excitatory effects led off to a galvanometer dur- 



ig definite periods at regular intervals after stimulation. 



ELECTRO-PHYSIOLOGY. 



Animals and plants have, as a general phenomenon, electricity, 

 ie potential energy of living matter. In the animal the nerves, 

 mscles, and glands are the special seats of the electrical properties, 

 muscle has three forms of energy work, heat, and electro-motor 



