1868.] Dr. W. H. Broadbent on the Action of Poisons. 



469 



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 probable that the affinities in 

 operation in the nervous structures of the frog are not sufficiently energetic 

 to determine the decomposition of the H Cy, which will then act upon 

 this animal as an anaesthetic. 



Nitroglycerine was at first made the subject of experiment, under the 

 idea that possibly oxygen might be evolved from the NO^, which is 

 substituted for three equivalents of H in the typical molecule. Sub- 

 sequent reflection showed that this is not likely to occur; but the 

 fact remains, that it is a substance liable to change, and very highly 

 charged with oxygen, as compared with the ordinary constituents of the 

 body. 



It is a very powerful poison, having, however, entirely different effects 

 on frogs and rats. 



In frogs it very speedily induces powerful tetanic convulsions (a single 

 drop of a solution of one pint of nitroglycerine in four parts of methyl in 

 alcohol placed on the back of a frog is followed in five or eight minutes by 

 stiffness of movement, and in thirteen to sixteen minutes by most violent 

 spasms). In rats an hour or more elapses before any symptom is manifest, 

 and then death is by a gradually increasing feebleness of movement, in 

 two or three hours, without convulsion. 



It is unquestionable that this difference in the effects has a relation with 

 the oxygen contained in the nitroglycerine. The contrast with prussic 

 acid in the action on warm and cold-blooded animals is suggested. 



A very extended and comprehensive inquiry, both as to the conditions 

 in the nervous system associated with convulsions, tetanus, delirium, &c., 

 and into the relations and constitution of the poisons which give rise 

 to these symptoms, is necessary before the second analogy can be followed 

 out with any confidence. Experiments are being made with substances of 

 known composition and constitution, with a view to elucidate this part 

 of tlie question. 



In conclusion, two points are considered which cannot be passed over in 



2 s 2 



