392 Royal Society : — 



probable that the affinities in operation in the nervous structures 

 of the frog are not sufficiently energetic to determine the decompo- 

 sition 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 N0 2 which 

 is substituted for three equivalents of H in the typical molecule. 

 Subsequent 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 con- 

 stituents 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 

 to the oxygen contained in the nitroglycerine. The contrast with 

 prussic acid in the action on warm and cold-blooded animals is sug- 

 gested. 



A very extended and comprehensive inquiry, both as to the con- 

 ditions 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 the question. 



In conclusion, two points are considered which cannot be passed 

 over in any attempt to apply the principles of physical and chemical 

 science to the case of poisons. 



The first is as to the minuteness of the fatal dose. Any expla- 

 nation, before it can be accepted, must show that the cause is adequate 

 to produce the effect. This is a difficulty in the path of any rational 

 explanation. It is attempted to meet it by showing, on the one hand, 

 that the equivalency of nerve-force is extremely small, by reference 

 to its analogy with electrical currents, and by other considerations, 

 and that therefore the degree of chemical change involved in its 

 evolution is also small ; and, on the other hand, the maximum of 

 force to be obtained from an organic body is through the exercise 

 of the affinities of its individual elements. 



The second point is as to the special action of certain poisons on 

 particular nervous centres — strychnia on the cord, morphia on the 

 brain, &c, the substances being carried by the blood to all alike. It 

 is as necessary to explain why no effect is produced on those centres 

 or tracts which do not suffer, as to explain the action on the one 

 which does. The explanation is sought in the fact that the differ- 



