PREFACE. 



THE following pages are intended to give the reader such 

 preliminary hints as to the subjects of the Memoirs which are 

 included in the present series of translations, as may aid him in 

 using the volume either for the purpose of extending his know- 

 ledge of the branch of physiology to which they relate, or of 

 obtaining information on special questions. It will be seen by 

 glancing at the Table of Contents, that the Memoirs refer to 

 three principal subjects, and that with one exception, that of 

 Prof, du Bois-Reymond's research on Malapterurus, all have 

 appeared within the last five years. 



The purpose of the investigation recorded in the first Paper 

 is to obtain a new proof of the well-known law established by 

 Pfluger in his classical research on Electrotonus, published in 1859, 

 relating to the changes of excitability of a nerve produced by 

 the flow along it of a voltaic current. In 1881 the Author invented 

 and described a new instrument, by which it is possible to subject 

 a nerve to instantaneous mechanical excitation, of which the in- 

 tensity can be measured and varied at will. When this is accom- 

 pli shed by the falling on the nerve of a weighted lever, it is found 

 that the nerve is so little damaged thereby, that the excitation 

 may be repeated as often as necessary without impairment of the 

 effect, and that its strength may be graduated by the observer 

 with an exactitude scarcely inferior to that which is attainable 

 in the use of induction currents. As a means of measuring the 

 excitability of a nerve, mechanical excitation has this great 

 advantage as compared with excitation by induction currents, 

 that it is free from those ' after-effects ' of which the nature is so 

 fully studied in the series of researches contained in Part II 



