' i"?0 Aiialogy between Vegetables and Animals 



ployed, its application is followed only by impaired irritability. 

 Again, if a strong dose of the infusion of belladonna be given 

 to a man, it occasions vertigo, sickness, convulsions, para- 

 lysis, and death ; if the same infusion be poured over a plant, 

 the leaves become affected with a sort of spasmodic action : 

 they then grow flaccid, and in the space of a few hours the 

 plant dies. Now, it has been long known that the poisonous 

 agents which I have named do not operate injuriously upon 

 the animal body by destroying its fibre, but by interrupting 

 the functions of the nervous system. It therefore seems pretty 

 evident that, since they act in the same manner on vege- 

 tables as they act on animals, the former must, like the 

 latter, be endowed with nervous structure. It has been a 

 question among physiologists to determine in what maimer 

 poisonous bodies produce their specific effects upon the 

 animal system. On this point several opinions have been 

 advanced. Majendie came to the conclusion that they were 

 absorbed by the veins, and passed directly into the circula- 

 tion. Brodie supposed that they sometimes operated by 

 entering the circulation, and at others by acting on the sen- 

 tient extremities of the nerves, and, through them, on the 

 brain. There are others, again, who imagine that they 

 indirectly enter the circulation by absorption through the 

 lymphatics, but that, before they can exert their specific effects 

 upon the general system, they must be brought into absolute 

 contact with the brain. Morgan and Addison, in an essay 

 published about fifteen months ago, argue " that all fair 

 analogy forbids the conclusion, that at one time a poison 

 shall be taken up by the veins, and carried through the cir- 

 culation to the brain, before it produces any sensible effect ; 

 that at another time the absorbent vessels shall take up the 

 substance, and, by their communication with the subclavian 

 veins, be thus instrumental in carrying the specific agent into 

 the circulation, and thence to the brain ; and again, at another 

 time, the impression made upon the extremities of the nerves 

 of the poisoned part shall at once, by the medium of those 

 poisoned nerves, be conveyed to the brain, independently of 

 absorption either by the veins or absorbent vessels. ... As 

 reasonably," say they, " might it be presumed, that at one 

 time the sense of taste was communicated by a branch of the 

 fifth pair of nerves, and at another time by the salivary 

 ducts, as to entertain a belief that veins, absorbents, and 

 nerves individually performed a function of precisely a simi- 

 lar nature." These gentlemen, therefore, after performing 

 many scientific experiments, conclude, and apparently with 

 great correctness, that all poisonous agents produce their 



