50 CONTRIBUTION TO THE 



showed that from this principle the law of contraction as he had 

 found it could be deduced with the greatest ease. 



The fact, that when the current is closed, excitation occurs at 

 the negative pole, connects itself with a number of purely physical 

 phenomena. Thus, for example, in the induction spark the electric 

 light shows itself only at the negative pole. In vacuo, the 

 negative pole is entirely surrounded with a beautiful violet light, 

 while the positive pole emits only a luminous crown of purple- 

 coloured rays. The temperature of the violet is higher than that 

 of the purple light. In the voltaic arc the light constantly appears 

 first at the negative pole, while the positive is yet dark ; presently 

 this too gets warmed up, small particles begin to pass over, and so 

 on (Neef, Ruhmkorff, Despretz, Moigno 1 ). 



We have therefore analogies derived from other sources, which 

 teach that, at least in some cases, the electric current acts most 

 powerfully at the negative pole. There are also facts which might 

 serve as analogies for the changes of excitability occurring at both 

 poles during the closure of a current. Thus Matteucci 2 , and after 

 him Eleischl 3 , found that, when nerves are treated with weak 

 alkaline solutions (-08 %), their excitability rises, and that, on treat- 

 ment with weak acids (-075 %) 5 it falls. Now we know that the 

 current gives off acids at its positive pole and alkalies at its nega- 

 tive. We have here, therefore, a complete agreement between the 

 changes of excitability elicited by the constant current and those 

 generated by the corresponding electrolytes. To these facts we may 

 add an old observation of Gustav Crusell's, who found that the or- 

 ganic tissues are coagulated at the positive pole, probably through the 

 formation of acids, and that the coagulum formed is again liquefied 

 by the negative pole, probably through the alkalies liberated there, 

 or in other words, the positive pole makes the structure of organic 

 tissues firmer, while the negative pole exerts the contrary action 4 . 



1 Daguin, Traite" e'le'mentaire de Physique, iii, Paris and Toulouse, 1879, PP- 

 47 2 -473. 



2 Matteucci, Comptes Kendus de 1'Acaddmie des Sciences, torn. 65, p. 155, 1867. 

 8 Fleischl, Archiv f. Anatomic und Physiologie, 1882, p. 17. 



* G. Crusell, Uber den Galvanismus als chemisches Heilmittel gegen ortliche 

 Krankheiten, St. Petersburg, 1841, p. 14 et seq. 



Among Crusell's experiments the following may be given here : ' If a galvanic 

 current from a small compound battery is led into the eye of a living animal by means 

 of a needle introduced through the cornea, after the current has been in operation 

 half a minute, a whole minute, or longer, according to the strength of the battery, 

 there occurs, often at once, at latest after some days, a clouding of the pupil, some- 

 times associated with a partial coagulation of the aqueous humour. If the galvanic 



