518 



REPORT — 1807, 



induces a change in the motor nerve cells upon which normally the con- 

 tinuous afferent activity plays in such a way as to render the connection 

 of the motor nerve cell closer with some afferent endings and less close 

 with others. 



If increase of resistance to conduction at a synapsis, that is at a place 

 of neural linkage, be due, therefore, to greater separation of nerve cell 

 from nerve cell by retraction of cell branches, I would urge that it occurs 

 in a very marked degree in the dendrite branches of the motor-cell of 

 the ventral horn of the spinal cord. 



IV. On the Action of Reagents njwn Isolated Nerve. By A. D. Waller, 

 M.D., F.R.S., and S. C. M. Sowton. 



A preliminary general account of the experiments we have made 

 during the past year in prosecution ^ of the investigation of the Action of 

 Reagents upon Isolated Nerve, may be given under the following heads : — 



§ 1. The influence of acids and alkalies upon currents of action. 



§ 2. The influence of acids and alkalies upon electrotonic currents. 



§ 3. The influence of carbonic acid and of tetanisation upon electro- 

 tonic currents. 



§ 4. The influence of alterations of temperature upon electrotonic 

 currents. 



§ .5. The action of some anaesthetics and of some alkaloids upon elec- 

 trotonic currents. 



§ 1. The influence of acids and alkalies upon currents of action. — 

 Experiments under this head were undertaken at an early stage of our 

 investigation. We soon realised, however, that it would be desirable to 

 postpone the prosecution of this branch of the subject until we should have 

 examined the more fundamental problems concerning the action of acids 

 and alkalies upon electrotonic currents (§ 2). The following summary 

 statement will, however, serve to convey an idea of the scope and tenor 

 of this first group of experiments :—[M= Molecular, ]Sr=N'ormal] 



Dilute acid solutions (M/40 to M/10) cause primary augmentation, 

 followed by secondary gradual diminution of the negative variation. 



Stronger acid solutions (M/10 to M/.5) cause primaiy diminution and 

 abolition of the negative variation. 



Alkaline solutions at all effecti\-e strengths (M/50 to M/5) cause 

 primary diminution and abolition. 



The eff'ect of an acid solution is not in proportion with its ' avidity.' 

 Approximately equal effects are produced by decinormal acetic, nitric and 

 sulphuric acids.- But in the case of some other acids, equinormal solu- 

 tions give markedly unequal effects. Thus phosphoric acid is less active, 

 and lactic acid is more active than nitric acid ; approximately equal effects 

 being produced by lSr/5 phosphoric acid, by N/lO nitric acid, and by N/20 



' An account of previous observations is given in the Phil. Trans. U.S. for 1897, 

 and in three papers published in 'Brain ' during 1896 and 1897. 



