THE RE-ACTIONS OF ORGANIC MATTER ON FORCES. 55 



marked effects on the brain, are not remarkably sapid — how- 

 ever true it may be that there are relations between par- 

 ticular substances and particular parts of the nervous system ; 

 yet such instances do but qualify, without negativing, the 

 general proposition. The truth of this proposition can 

 scarcely be doubted when, to the facts above given, is added 

 the fact that various condiments and aromatic drugs act as 

 nervous stimulants; and the fact that anaesthetics, besides 

 the general effects they produce when inhaled or swallowed, 

 produce local effects of like kind — first stimulant and then 

 sedative — when absorbed through the skin ; and the fact that 

 ammonia, which in consequence of its extreme molecular 

 mobility so quickly and so violently excites the nerves be- 

 neath the skin, as well as those of the tongue and the nose, 

 is a rapidly-acting stimulant when taken internally. 



Whether a nerve is merely a conductor, which delivers at 

 one of its extremities an impulse received at the other, or 

 whether, as some now think, it is itself a generator of force 



by implication, relatively unstable bodies. The small amounts of molecular 

 change which take place in these small quantities of the vegcto-alkalies when 

 diffused through the system, initiate larger amounts of molecular change in 

 the nitrogenous elements of the tissues. 



But the evidence furnished a generation ago by these vegeto-alkalies has 

 been greatly reinforced by far more striking evidence furnished by other 

 nitrogenous compounds — the various explosives. These, at the same time 

 that they produce by their sudden decompositions violent effects outside the 

 organism, also produce violent effects inside it: a hundredth of a grain of 

 nitro-glycerine being a sufficient dose. Investigations made by Dr. J. B. 

 Bradbury, and described by him in the Bradshavv Lecture on "Some Ne'v 

 Vaso-Dilators " (sec TJie Lancet., Nov. 16, 1895), details the effects of kindred 

 bodies — methyl-nitrate, glycol-dinitrate, crythrol-tetranitrate. The first two, 

 in common with nitro-glycerine, are stable only when cool and in the dark — 

 sunlight or warmth decomposes them, and they explode by rapid heating or 

 percussion. Tlie fact which concerns us here is that the least stable — glycol- 

 dinitrate — has the most powerful and rapid physiological effect, which is pro- 

 portionately transient. In one minute the blood-pressure is reduced by one- 

 fourth and in four minutes by nearly two-thirds: an effect which is dissipated 

 in a quarter of an hour. So that this excessively unstable compound, decom- 

 posing in the body in a very short time, produces within that short time a vast 

 amount of molecular change: acting, as it seems, not through the nervous 

 system, but directly on the blood-vessels. 

 5 



