66 STUDIES IN ELECTRO-PHYSIOLOGY: 



are found who yield a positive and three a negative re- 

 action. If the observer himself is of positive sign two 

 other positives only will be required, and vice versa. Then 

 let the testing-room be vacated for several hours and freely 

 ventilated. 



As a next step introduce each of the persons selected to 

 the testing-room, one by one, " earth " the subject for five 

 minutes, and take the hand-to-hand deflection very care- 

 fully, noting the sign and number of millimetres and 

 ushering the subject from the room before the next one is 

 admitted. 



Let us assume that the deflections are respectively as 

 follows : 



Observer = 250 mm. positive 



First subject = 200 



Second ,. = 225 



Third = 250 negative 



Fourth -200 



Fifth =225 



These figures might not actually obtain in practice, 

 but they will serve to illustrate my meaning and are 

 sufficiently near to the truth. 



Having registered the above data, let the observer and 

 the five subjects assemble in the testing-room and remain 

 together for a few hours, the length of time being dependent 

 upon the size of the room and its insulation from the earth. 

 If it is of moderate dimensions, carpeted, and with doors 

 and windows closed, two hours should be sufficient. Then, 

 without earthing and without anyone leaving the labora- 

 tory, take the hand-to-hand deflections again, in the same 

 order. 



Now, if the differences in polarity and in the number of 

 millimetres exhibited by the subjects are due to dis- 

 similarity of metals, acted upon by different secretions of 

 the sweat-glands, the deflections should be as before, 



