390 Royal Society : — 



troduction into the molecule of methyl-iodide, carrying back the 

 constitution a step in the direction of the ammonium type, the 

 poisonous effects are greatly diminished, and entirely altered in cha- 

 racter. 



Let the deduction as to the evolution of nerve-force be accepted, 

 and we have in the introduction into the blood of substances having 

 varying degrees and directions of tension an intelligible method of 

 influencing its manifestations. 



Looking now upon nerve-action as a result of oxidation, in the 

 various methods by which this oxidation may be influenced, analo- 

 gies may be traced with conditions which affect ordinary combustion. 

 These conditions are : — 



1 . The supply of oxygen. 



2. The character of the combustible. 



3. The presence of products of combustion, or of bodies having a 

 similar influence. 



It is of course necessary to bear in mind the peculiarities of the 

 oxidation yielding nerve-force, the differences between combustion 

 and oxidation in the moist state, and the special modifying condi- 

 tions of the animal organism. For example, while in asphyxia the 

 deprivation of oxygen arrests all nervous action, the respiration of 

 undiluted oxygen does not intensify it, either because the blood will 

 only take up a certain proportion of oxygen, or more probably be- 

 cause the effects of the O are expended in altering the blood, which 

 is thus oxidized instead of being oxygenated. 



The analogies to the above conditions found in the action of sub- 

 stances on the nervous system are : — 



1. The liberation in the nascent state in the nervous structures of 

 C and H, which appropriate the O brought by the blood, and so pro- 

 duce a result equivalent to the exclusion of O. The C and H are 

 set free by the dislocating influence of N ; and the example of this 

 mode of action is furnished by prussic acid. 



The converse of this, the liberation of O by a similar process, is 

 not likely to occur, as O is never present in an organic body in 

 excess of the proportion which would fully oxidize the other ele- 

 mentary constituents. 



2. The analogy to the influence on the energy of combustion by 

 the character of the combustible, is found in the introduction into the 

 blood of substances having chemical tension, holding different rela- 

 tions to the tension of the nervous matter. 



3. The action of anaesthetics on the nervous system furnishes a 

 strict parallel to the influence of C0 2 on combustion. 



The rationale here given as to the action of anaesthetics is, for the 

 purposes of the present paper, taken as established by the late Dr. 

 Snow. Objections which have been made -to it are capable of re- 

 moval by experiments and considerations which need not here be 

 adduced. 



Considerable importance is attached to the establishment of the 

 explanation here given of the action of prussic acid. Stated more 

 explicitly, this explanation is, that the prussic acid is carried by 

 the blood to the nerve-centres, that, under the influence of the affi- 



