CHAPTER XXVII. 

 ELECTRICAL CONSIDERATIONS. 



Elrcti'ii'ifii i-oiiiex under consideration in Physiology as follows : 



1. As a convenient stimulus for muscles and nerves in the form of induction 

 currents. 



2. As a direct battery current for the production of polarisation in nerves and 

 exceptionally in this orm as a stimulus. 



3. As a direct battery current for actuating mechanical contrivances, such as 

 time markers, &c., the basis of which is the electromagnet. 



4. The passage of a current through a conductor in the proximity of a magnetic 

 needle causes the needle to move. This principle is made use of in the galvanometer 

 and by means of it the currents yielded by living tissues can be recognised and 

 measured. 



Remember: Electromotive force (E.M.F.) is the force which tends to move 

 electricity from a point of higher to one of lower potential. The unit of E.M.F. is 

 the volt, and is therefore the measure of electrical pressure. One volt will move a 

 quantity of 1 coulomb of electricity through a resistance of 1 ohm in 1 second, 

 thereby producing a current of 1 ampere. This relationship is expressed by the 

 B 



Current (amperes)^ Total F.M.F. (in volts)^ 

 Total Resistance (in ohms). 



DANIELL 



CELL 



POLARISATION 



<;. -in. '['lie tilm of H, which produces p 

 C plate of the simple cell. 



DEPOLARISAT10N 



>larisati<m, is shown as a row of dots 



The galvanic cell consists of two plates or elements, commonly 

 the one of zinc and the other of carbon or copper immersed in a 

 sensitising fluid (l()i lc - H.,S0 4 ). The action of the cell depends upon 

 the solvent action of the acid upon the zinc, zinc sulphate being formed. 

 At the same time H is liberated. This transaction is pictured in the 



