104 -47V INTRODUCTION TO ZOOLOGY. 



abandoned. Tlie following explanation of the facts 

 has been offered. The electric currents noticed in a 

 severed mascle or nerve when at rest are due to the 

 electric interaction of dead and living tissue, of which 

 the latter has a higher state of electric potential ; and 

 precisely similar currents are shown by sections of 

 vegetable tissues : it has been proposed to give to these 

 currents the general name of boundary currents. 

 Their existence depends upon the injured parts of the 

 severed structure being in a dead or dying state, while 

 the middle and uninjured parts remain alive. The 

 electric changes noticed ia a nerve or muscle stimu- 

 lated to activity are due to a similar interaction 

 between resting and active tissue, in which the resting 

 part would appear to have the higher potential. The 

 stiffness of the active muscle seems to be in a way 

 comparable to the stiffness of death as regards its 

 electric condition; and it is considered possible that 

 the chemical conditions of the two may also be to a 

 slight extent similar. To these currents that take 

 place in active tissues, it has been proposed to give 

 the name of functional currents : they are more 

 complicated in their nature tliau the boundary 

 currents. It is important to notice that similar 

 currents take place with variations of temperature, the 

 electric potential of warm tissue being greater than 

 that of colder tissue. 



It will easily be seen from the above statements, 

 that our present knowledge of the electric conditions 

 which have really been demonstrated to exist in 



