ON THE DIARRHŒA WHICH AFFECTED THE BRITISH ARMY IN THE CRIMEA IN 1854—55
42 indirect action of strychnine is not limited to one particular part of the cord. It appears strange that the poison, when directly applied to the spinal cord, did not affect the nerve substance through entering it, either by imbibition or deosmose. Can it be possible that poisons deosmotically absorbed are not assimilated by the nervous system ? or do they first require to undergo a change in the blood before they can act? That strychnine should produce convulsions when carried to the spinal
... rried to the spinal cord by the bloodvessels, and not when directly applied, is certainly very remarkable. The solvent in each case is the same, the liquid part of the blood being nothing more or less than water, and the bloodvessels cannot bring the poison into more intimate connexion with the nerve-tubes than the hand can; for the ultimate capillaries do not enter the nerve-tubes, but only ramify on their exterior. If, therefore, the poison really acts upon the contents of the nerve-tubes, it must, to reach their interior, first pass by deosmose through the external sheath; and deosmose being a purely physical process, it matters not how, or by what means, the substance is brought into contact with the membranous tube of the nerve ; for once there, its after-progress is in all cases identical. Now, as we have brought strychnine into the most favourable circumstances for the development of its action upon nerve substance, and no result has followed, we are forced to conclude that strychnine has no direct chemical or physical action on nerve matter. Seeing that the poison acts when conveyed by the bloodvessels, we must try and discover whether or not it is transformed in the blood into a more active poison, or if, though not itself transformed, it yet possesses the power of so modifying the organic constituents of the blood, as to render them not only useless for the purpose of nutrition, but even pernicious. Chemistry has as yet failed to reveal whether or not strychnine is decomposed and transformed in the blood into another substance more baneful than itself; but it has shown,* that the poison possesses the property of so modifying the organic constituents of the blood as to render them incapable of absorbing oxygen, and exhaling carbonic acid, and thus becoming fitted for the purpose of nutrition. It is well known, that " the continual afflux of scarlet blood is a condition very important to the normal molecular constitution of the nervous centres. This proposition especially holds good with mammals and birds; but is less Strictly applicable to reptiles and fishes, in whom the interchange of the gases is less active. "t When the oxidized materials required as nourishment by the nervous system are either deficient in quantity, or impaired in quality; disordered function of the nerves is the immediate result. We have a most striking example of the former condition in cases of hæmorrhage, where an insufficient supply of the oxidized substances is not unfrequently followed by convulsions; the latter is exemplified in cases where oxygen is prevented from entering the blood, and consequently the organic substances fail to become oxidized and fitted for their peculiar office. Lastly, the same thing occurs when even both the oxygen and the organic substances are present, but where the oxidizing process is either partially or totally arrested by the presence of a foreign substance possessing the property of hindering the constituents of the blood from combining with oxygen. Derangement in the function performed by the molecules of the nervous system occurs just as surely in the latter example as when either the oxygen alone, as in the second instance, or both the oxygen and the oxidizable materials, as in the first case, are wanting. Strychnine, I believe, from the results of the cited experiments, acts in the third of the three ways-that is to say, it has no immediate effect upon the nervous system, but acts indirectly through the power it possesses over the functions of the organic constituents of the blood. Many other poisons, I doubt not, exert their influence in a similar manner; for I have found, that hydrocyanic acid, chloroform, nicotine, alcohol, ether, morphine, and several other narcotics, have the same power of destroying the property possessed by the organic constituents of the blood of absorbing oxygen and exhaling carbonic acid. A more particular study of the effects of different substances on the blood may yet not only furnish a clue to the actions of poisons in particular, but afford a direct explanation of the physiological action of remedies in general; and the more speedily our knowledge in that direction advances, the more rapidly will medicine be raised to its proper position amongst the inductive sciences.