PHYSIOLOGY OF NERVE 



One possibility may be dismissed from the mind. As far as 

 our present knowledge goes, these curves are not current escape 

 or any error of the apparatus. They are abolished by ligature of 

 the nerve, by touching the nerve with ammonia, and by " electro- 

 cution." If the peripheral end of the other vagus is stimulated, 

 the cardiac waves disappear, as the heart is stopped, while the 

 respiratory waves continue, as can be seen in Fig. 4. In apnoea, 

 the cardiac continue and the others cease. 



Both the E.M.F. and the time relations of these curves agree 

 with the older observations with the electrometer. Alcock and 

 Seeman (loc. cit.) give the E.M.F. of the respiratory response 

 as '00005 to '0002 volts, and the time as about 4 sees. ; the 

 maximum on prolonged inflation of the lungs as -00025 volt. 



What, then, is the explanation ? The differences in potential 

 may be due (and to some extent are certainly due) to the fact 

 that only a few of the fibres of the nerve are in action at any 

 one time, but how is the difference in time to be accounted for ? 

 There are several possibilities. These long waves of small E.M.F. 

 might be the algebraic sum of many short waves ; and if we had 

 the electrometer records alone to go by, these might be too slow 

 to indicate the successive teeth of such a curve. But there is no 

 trace of such a summation in the string galvanometer photograph, 

 although the instrument is sensitive and quick enough to detect 

 000005 volt lasting for the y^ of a second. Further, this instru- 

 ment is free from the peculiarity of the electrometer that shows 

 the effect of equal alternate currents of short duration as a dis- 

 placement of the meniscus in the direction of the sulphuric acid. 

 The exact relation of these two phenomenon which we have called 

 by the name of negative variation is therefore one of the pro- 

 blems still awaiting solution, and we have only the suggestion 

 by Einthoven that possibly his curves are more nearly related to 

 the electronic currents than to the short steep curves the result 

 of single induction shocks, that Gotch has analysed in the sciatic 

 of the frog. 



Einthoven finally gives a very interesting photograph showing 

 the variations in potential in the uninjured vagus as a result of 

 the various nerve impulses passing both up and down the nerve. 

 The exact analysis of the course is, however, so complex that we 

 must await the result of future work before we understand the 

 full meaning of the photograph. 



