Dr. W. H. Broadbent on the Action of Poisons. 389 



action, it is necessary to consider closely the evolution of nerve-force, 

 and to endeavour to realize the chemical conditions implied. 



In the first place, the source of nerve- force is oxidation, and the 

 seat of the oxidation is the nervous structures. This is generally 

 admitted, and seems to be conclusively established by an analysis 

 of the phenomena observed in experiments with a prepared frog's leg. 



This admitted, it is to be noted — 



1. That nerve-action is intermittent and of varying intensity, and 

 that, in addition to the presence of the oxygen brought to the nerve- 

 structures by the blood, an impulse from without, or from some 

 other part of the nervous system, is necessary to determine the evo- 

 lution of the force. 



2. Again, there is a storing up of potential energy in the nervous 

 structures ; witness the necessity for sleep, &c. 



3. A due supply of oxygen is required. The phenomena of 

 asphyxia show that the demand is most urgent in the hemispherical 

 ganglia. 



These facts indicate that the constituent of the nervous structures 

 by oxidation of which the force is yielded, possesses what I have 

 ventured to call chemical tension, a property which does not belong 

 to non-nitrogenized matter, or to all nitrogenized matter. It will 

 be further explained later ; for the present, it is sufficient to refer to 

 nitroglycerine as an extreme example. 



The protagon of Liebreich, and the neurine recently identified by 

 Wurtz with hydrate of trimethyl-oxethyl-ammonium, have this cha- 

 racteristic in a certain degree. 



Turning now to the poisons which kill by their powerful action on 

 the nervous system. They all contain nitrogen, and all possess che- 

 mical tension ; and these seem to be the only points common to the 

 entire group. 



Nitrogen cannot be the poisonous element ; it has no great che- 

 mical energy, and it is present in large proportion in substances 

 which are inert. It is nevertheless the pivot on which the deadly 

 influence turns. Its affinity for H, O, and especially for C, is only 

 feeble. When, therefore, in a molecule containing C, H, and N, or 

 C, H, N, and O, the elements are not so arranged that the mutual 

 affinities of C, H, and O cooperate to maintain the integrity of the 

 molecule ; there may be a more or less powerful tendency on the part 

 of C, H, and O to rearrange themselves without regard to the N, or 

 to combine with O or H 2 O if presented. This is what is meant by 

 the term chemical tension. In the example given, nitroglycerine 

 {C 3 H 5 (N0 2 ) 3 3 }, the dislocation is of O from N in favour of C and 

 H. Equally striking examples of dislocation of N from C or H can- 

 not be given, and it is not easy in all cases to point out the source of 

 the tension. A very important method in which the balance of affi- 

 nities is deranged and the condition of tension brought about, is by 

 departure from a stable type, as, for instance, in the nitrite bases 

 which are residues derived from ammonium-salts by dehydration. 

 To this class belong morphia, strychnia, brucia, and most poisonous 

 alkaloids. Additional interest is given to these compounds by the 

 fact that Dr. Crum Brown and Dr. Fraser have shown that, by in- 



