468 Dr. W. H. Broadbent on the Action of Poisons. [June 18, 



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

 substances having chemical tension, holding different relations to the tension 

 of the nervous matter. 



3. The action of ansesthetics on the nervous system furnishes a strict 

 parallel to the influence of CO^ on combustion. 



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

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

 Objections which have been made to it are capable of removal by experi- 

 ments and considerations which need not here be adduced. 



Considerable importance is attached to the establishment of the expla- 

 nation 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 affinities thus brought to 

 bear upon it (affinities which normally determine the oxidation by which 

 nerve-force is evolved), its elements are dislocated from each other, and 

 the C and H liberated in the latent condition appropriate the O destined 

 for the evolution of nerve-force which is thus arrested. 



This explanation is suggested by the composition of hydrocyanic acid, 

 H Cy. Cyanide of potassium KOy, again, is used as a powerful re- 

 ducing agent in chemical processes. Its liability to the change which 

 will permit its elements to exercise their individual affinity for O, is indi- 

 cated by its spontaneous decomposition in water, by its position as a nitrile 

 (formio-nitrile). Corroborative evidence that it is by means of such a 

 change that it acts, is furnished when the elements are held together by 

 some supporting affinity, as in ferro-cyanogen. But the best example is 

 in sulphocyanogen and hydrosulphocyanic acid, which of themselves are 

 poisonous (z. e. cannot resist the dislocating influences), but, reinforced 

 by a base, are innocent. [A parallel to this is seen in aniline, which is 

 poisonous, and in sulphate of aniline, which is not. See Lond. Hosp. 

 Reports, Dr. Letheby.] 



The phenomena by poisoning by prussic acid are perfectly consistent 

 ■with this view. All observers have noted their similarity to those of 

 asphyxia. 



Still more striking is the fact that artificial respiration, and espe- 

 cially with oxygen, is the great means of neutralizing the effects of this 

 poison. 



Probably this chain of facts would be considered conclusive, were it not 

 that the hypothesis as to the mode of death by H Cy is paralysis of the 

 respiratory movements. This hypothesis, however, still leaves unexplained 

 the cause of the paralysis itself, and therefore the real mode of action of 

 the poison. It is, moreover, inconsistent with certain of the phenomena ; 

 the respiratory nerve-centres are actually the last to be paralyzed, except 

 those concerned in the action of the heart. 



Experiments nevertheless have been made for the purpose of ascertaining 

 whether the previous respiration of undiluted oxygen would retard, or in 



