MINERAL POISONS. 85 



symptoms which arise from the action of the 

 poison on the stomach and intestines. There is 

 no difference in the effects of arsenic, whether it 

 is employed in the form of oxyde, or of arseniac 

 acid, except that the latter is a more active pre- 

 paration. When arsenic is applied to a wound, 

 the symptoms take place sooner than when it is 

 given internally ; but their nature is the same. 



The symptoms produced by arsenic may be 

 referred to the influence of the poison on the 

 nervous system, the heart*, and the alimentary 

 canal. As of these, the two former only are 

 concerned in those functions which are directly 

 necessary to life ; and as the alimentary canal is 

 often affected only in a slight degree, we must 

 consider the affection of the heart and nervous 

 system as being the immediate cause of death. 



In every experiment which I have made with 



* When I say that a poison acts on the heart, I do not mean 

 to imply that it necessarily must act directly on the muscular 

 fibres of that organ. It is highly probable, that the heart is 

 affected only through the medium of its nerves ; but the affec- 

 tion of the heart is so far independent of the affection of the 

 nervous system generally, that the circulation may cease, 

 although the functions of the brain are not suspended, and 

 the functions of the brain may be wholly suspended without 

 the circulation being at all disturbed. In proof of the first of 

 these propositions, I may refer to my former experiments on 

 the upas antiar, in which the sensibility of the animal con- 

 tinued to the very instant of death ; and respiration, which 

 is under the influence of the brain, continued even after the 

 heart had ceased to act. In proof of the second, I may refer, 

 among many others, to the experiments detailed in the 

 Croonian Lecture for 1810. 



G 3 



