250 STUDIES IN ELECTRO-PHYSIOLOGY: 



(3) The hands, after " earthing," must be washed with 

 soap and water, and not only dried with a towel but given 

 an interval of at least five minutes before testing. 



(4) During the time that the subsequent testing of 

 the body takes place it is desirable that the number of 

 persons in the testing-room should be limited to the 

 patient and the observer. But this is not always possible. 

 In certain cases a medical attendant and a female friend or 

 a nurse must be present, but in these cases such persons 

 should be stationed as far from the patient as possible, and 

 not admitted to the testing-room until the hand-to-hand 

 deflection, both as regards sign and quantity, has been 

 accurately determined. 



APPLICATION OF OHM'S LAW TO SOLUTIONS. 



Where E = E.M.F., and / is the distance between 

 electrodes. 



Generally speaking, " the velocity of the ions is pro- 



F 



portional to the value of the motive force -j ." 



Such a law as that " the velocity with which a particle 

 moves under the influence of a certain force is proportional 

 to this force " is valid for all liquid or gaseous particles 

 moving between other liquid or gaseous particles so long as 

 collisions constantly take place. This law can be derived 

 from the principles of the kinetic theory of gases, as is 

 proved in treatises on internal friction. 



" We must imagine the ions as particles of a liquid 

 which receive an acceleration under the influence of some 

 external force, electrical or osmotic, and the velocity im- 

 parted is proportional to the force acting. The ions, like 

 liquid particles in general, become more mobile as the 

 temperature rises." (Arrhenius.) 



