Dr. W. H. Broadbent on the Action of Poisons. 391 



nities thus brought to bear upon it (affinities which normally deter- 

 mine the oxidation by which nerve-force is evolved), its elements 

 are dislocated from each other ; and the C and II, 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 KCy, again, is used as a power- 

 ful reducing agent in chemical processes. Its liability to the change 

 which will permit its elements to exercise their individual affinity for 

 O is indicated by its spontaneous decomposition in water, by its po- 

 sition as a nitrile (formio-nitrile). Corroborative evidence that it is 

 by means of such a change that it acts, is furnished when the ele- 

 ments are held together by some supporting affinity, as in ferro- 

 cyanogen. But the best example is in sulphocyanogen and hydro- 

 sulphocyanic acid, which of themselves are poisonous (i. e. cannot 

 resist the dislocating influences), but reinforced by a base are in- 

 nocent. [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 of poisoning by prussic acid are perfectly con- 

 sistent 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 para- 

 lysis 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 as- 

 certaining whether the previous respiration of undiluted oxygen would 

 retard, or in any measure prevent the action of prussic acid. The 

 results have been by no means uniform ; but instances have occurred 

 (rats being the animals used) in which, after the injection of an 

 overwhelming dose, the fatal effect has been delayed quite beyond 

 the operation of accidental causes, and, again, in which a dose fatal 

 to two rats, and barely survived (after a long train of symptoms) by 

 one other, produced comparatively little effect on another after the 

 respiration of oxygen. 



It has been found also that a proportion of prussic acid diffused 

 in equal volumes of air and of oxygen, has a decidedly less powerful 

 action on the animal in the latter case. 



With frogs the results were most contradictory and embarrassing, 

 till it was discovered that prussic acid injected under the skin had 

 scarcely any action on them ; but if they were subsequently placed 

 under a glass shade, or in some other confined atmosphere, into 

 which the acid diffused, it would gradually affect them. It seems 



