PREFACE. V 



well-ascertained relations between the strength of the former 

 and that of the latter (see Introduction to Griitzner's paper); 

 and (2) the numerous cases in which excitation at the anode 

 results, not from break of the current, but from sudden diminu- 

 tion of its strength. In these the varieties of effect which are 

 observed are, in Griitzner's opinion, such as point to polarisation, 

 not subsidence of anelectrotonus. How far this way of looking 

 at the subject is justified, the reader will be able to judge after 

 studying the criticisms of Prof. Hermann and Prof, du Bois- 

 Reymond. 



In No. 5, Prof. Hering has investigated the excitation of motor 

 nerves by voltaic currents from an entirely different point of 

 view. More than thirty years ago du Bois-Reyinond showed by 

 a remarkable experiment (see p. 128), in which he used no 

 apparatus excepting 'physiological clay,' that is, clay kneaded with 

 'normal' salt solution instead of water, that. if the cut and natural 

 surfaces of a nerve-muscle preparation are bridged, the muscle 

 contracts when the bridge is completed, and again when it is 

 broken. Starting from this observation, the author proceeds to 

 illustrate, by a variety of new modes of experiment, the exciting 

 influence exercised on nerve by its own current. He shows, for 

 example, that the mere falling of the end of a nerve on a moist 

 conductor (p. 130) produces contraction when the contact is of 

 such a nature as to bridge the two surfaces, that by this means, 

 if the contact is repeatedly made and broken, a tetanus ' without 

 metals ' may be produced, and that a real ' secondary twitch from 

 nerve ' is obtainable when one of two nerves is excited, of which 

 the two ends are applied to each other with their cut surfaces in 

 the same plane and looking in the same direction. When this is 

 the case, the muscle to which the unexcited nerve belongs re- 

 sponds to excitations of a distant part of the other by currents of 

 minimal intensity. In this respect the phenomenon may be con- 

 trasted with du Bois' 'paradoxical twitch,' which, as is well 

 known, only appears when the exciting currents are strong, and 

 led in in pretty close proximity to the contact between the 

 two nerves. He finally shows how the effects of opening and 



