1890.] 



Observations on Isolated Nerve. 



311 



Mercuric chloride is the most lethal of any salts hitherto tested ; 

 its M/100 solution abolishes the response. 

 Isomeric compounds differ in efficacy. 



Of the three dioxybenzenes, pyrocatecbin is tbe most and. hydro- 

 quinone tbe least toxic. 



Alkaloids and Narcotic Drugs. — The most obviously effective, so far, 

 have been cocaine, pbysostigmine, and aconitine (chloral hydrate 

 and butyl chloral hydrate ) ; the most ineffective morphia, atropine, 

 muscarine. 



Extract of opium is more effective than tartrate of morphia. 



Aconitine hydrochlorate is more effective than aconine, or pyra- 

 conitine, or pseudaconitine, or benzaconine ; and. there is a close 

 resemblance between the effects of aconitine and of acetic acid, 

 attributable to the acetyl group. 



3. Action of C0 2 on Nerve and Production of C0 2 hy Nerve. 



Carbon dioxide, the chief terminal product of protoplasmic action, 

 has been the object of detailed investigation, more especially with 

 reference to the question of its production during the excited activity 

 of nerve.* 



A small amount of C0 2 — such as is contained in e.g., expired air — 

 causes a marked augmentation of the negative variation. An isolated 

 nerve acts thus as an indicator of the presence of C0 2 . 



From which it was argued that if any C0 2 is produced within the 

 active (tetanised) nerve, a similar augmentation should occur. This 

 has since been verified under various conditions. 



The evidence is extended by further experiments on nerve in 

 various stages, giving various kinds of electrical response to the 

 same kind of excitation. 



An isolated nerve (in autumn and early winter) considered with 

 reference to its freshness presents three stages, in which the electrical 

 response is as follows : — 



I. A predominant negative effect. 

 II. „ „ positive after-effect. 



III. „ „ ,, effect. 



The effects of " little " C0 2 , and of tetanisafcion lasting five minutes, 

 upon nerve in these three states are as follows : — 



I. Augmentation of negative deflection. 

 II. Appearance of negative deflection. 

 III. Substitution of negative for positive deflection, or diminution 

 of positive deflection. 



* ' Physiol. Soc Proc.,' January, 1896. 



