VOL. LXX.] PHILOSOPHICAL TBANSACTIONS. Qog 



It is true, that death happens so suddenly after introducing the American 

 poison into the vessels, that we cannot well comprehend how it can take place in 

 so short a time ; for it may be said, that the poison is hardly arrived at the heart 

 before the animal is dead : nor is it well understood, how cold-blooded animals 

 can be killed by it (frogs, for instance, which live so long with the circulation 

 stopped) though it be true that they die much slower by these poisons than other 

 animals, whose blood is warm. A humour, or the blood's being affected by a 

 poison, may by degrees produce, in cold-blooded animals, disorders still greater 

 than those which may be caused by stopping the circulation. By death taking 

 place immediately on introducing the poison into the blood, we may be induced 

 to suspect, that there exists in that fluid a very active, subtle, and volatile prin- 

 ciple, which eludes the acutest sight, and even the microscope itself. This prin- 

 ciple may on this hypothesis appear necessary to life, and against this principle 

 the poison may be supposed chiefly to direct its operation. 



That there really exists in the blood a very active and volatile principle, may 

 very well be suspected from seeing that the poison of the viper prevents the 

 coagulation of the blood when it is drawn from the vessels, while, on the con- 

 trary, it produces a coagulation of it within the vessels. It may be supposed 

 tliat something evaporates from the blood when it is drawn out, which exists in 

 it while within the vessels. On this hypothesis this active and vital principle 

 may be considered as the result of the whole animal economy, not excluding the 

 nerves, which may mostly contribute to it. But all this is only mere conjecture, 

 more or less probable, and unsupported by experiment. We ought to abide by 

 sure facts, let the mode of explaining them be what it may. Now these facts 

 are, that the American poison does not act on the nerves, and that its action is 

 entirely on the blood. 



Before my experiments, no person would have doubted but that the action of 

 the American poison was immediately on the nerves. All the external signs de- 

 clared it to be so. These signs then are equivocal, and they are falsely adopted 

 by physicians for the certain proofs that a disease is purely nervous. All these 

 symptoms may exist without the nerves being in the least affected : the alteration 

 of the blood alone is sufficient to produce them in a moment. The principal 

 physicians have attributed the disease produced by the poison of the viper, and 

 by the American poison, to an alteration in the nerves ; it belongs to them now 

 to examine, whether other diseases, supposed generally to be nervous, be not 

 rather diseases of the fluids, than diseases of the blood. The suspicion is great, 

 the signs equivocal ; the principle is shown not to be general. I would not here 

 assert, that no disorder could ever be derived from the nerves ; this would be 

 running into one extreme in order to avoid another. There is no doubt but that 

 many diseases are nervous in their origin, and that many others become so from 



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