on the Action of Poisons on the Animal System. 213 
the region of the abdomen ; preternatural secretion of mucus 
from the alimentary canal ; sickness and vomiting in those 
animals, which are capable of vomiting ; 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 white oxide, or of arsenic acid, except 
that the latter is a more active preparation. 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 arsenic, there 
were evident marks of the influence of the poison on all the 
organs which have been mentioned ; but they were not in all 
cases affected in the same relative degree. In the dog, the 
affection of the heart appeared to predominate over that of the 
* When I say that a poison acts on the heart, I do not mean to imply that it neces- 
sarily 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 affection 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 ex- 
periments on the upas antiar, in which the sensibility of the animal continued to the 
very instant of death; and respiration, which is under the influence of the brain, con- 
tinued even after the heart had ceased to act. In proof of the second, I may refer, 
among many otners, to the experiments detailed in the Croonian Lecture for 1.810^ . 
