LECTURE VII 



Observations on the Human Skin Du Bois-Reymond's Experiments 

 Tarchanoffs Observations Sweat-prints Introduction of Ions through 

 the Skin. 



EXPERIMENTS by which electro-motive reactions are sought to 

 be demonstrated on the human subject are full of pitfalls, and 

 beset with fallacies. I do not consider that any one of the three 

 principal experiments I am about to show you ought to be re- 

 garded as convincing or conclusive, and it is mainly as an exercise 

 in criticism that they have been prepared for demonstration. 



A monotonous series of successful experiments is against all 

 nature ; lecture-table discoveries are never as easy as they are 

 made to appear ; there is often more real instruction in " failure " 

 than in " success." 



70. A fruit/ess "experiment." More than one person, 

 on learning that a blaze-current is a characteristic sign of life, 

 has said this : " Will my finger give a blaze-current if I place 

 it between those electrodes : it is alive I suppose ? " To which 

 question the obvious reply is, " Try it." In some cases the 

 "student "has said, "Oh, I don't like electric shocks," and his 

 research has terminated at this point. But if of a more inquir- 

 ing type, he has perhaps placed a finger between the electrodes, 

 and thereby experienced a first difficulty in this simple-looking 

 experiment. He cannot keep his finger absolutely still between 

 the electrodes, and the galvanometer spot wanders aimlessly 

 to and fro on the scale. The " research " may stop here ; the 

 "student" has to catch a train; his scientific curiosity is satis- 

 fied. A third student having cleared the first (imaginary) and 

 second very real and most obstructive fence, keeps his finger fairly 

 quiet between the electrodes, so that it is possible to neutral- 

 ise the accidental effects occurring between electrodes and skin, 

 and get the galvanometer spot fairly steady at or near its zero 

 point. An induction shock may now be passed through the 



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