Page:Proceedings of the Royal Society of London Vol 1.djvu/417

Rh this indeed appears but a feeble tribute of respect to the services which he has rendered to the science of mineralogy.

Since the crystallization of certain mineral substances, in which nothing but earths has been discovered, has appeared problematical to many persons, and has led to the supposition of the existence of unknown acids in their composition, Mr. Smithson endeavours to explain this difficulty, by suggesting that quartz itself may be considered as an acid, to which class of bodies it has analogous qualities : we shall then have a numerous class of silicates, both simple and compound; and zeolite will belong to the latter, and may be regarded as a hydrated silicate of alumina.

The substances selected for these experiments are vegetable poisons only ; and they were chosen of the most active kind, that the exact nature of their effects might be more readily discerned. The principal object of the experiments is to determine on which of the vital organs the inﬂuence of each poison is exerted, and through what medium the organ becomes affected. The ﬁrst series of experiments relates to the effects of internal application to the tongue and alimentary canal, and the second to the consequences of application to external wounds.

When proof spirit was given to a rabbit in sufﬁcient quantity to kill it, the heart was observed to continue in action after apparent death.

The same observation was made respecting the heart of a cat, killed by injecting the root of aconite into the rectlnn.

When the oil distilled from bitter almonds was employed, although no more than a single drop had been given to a cat, she died in five minutes. Two drops of the same oil injected into the rectum of an- other cat, killed it also in five minutes. And the heart, in each in- stance, continued acting nfter apparent death.

Distilled oil of tobacco exerted nearly the same energy as the distilled oil of bitter almonds, and apparently in the same way, as the heart was observed to contract after apparent death.

From this circumstance, Mr. Brodie inferred that these poisons exert their primary inﬂuence on the brain, and that death ensues in consequence of the suspension of respiration, which is dependent on the brain.

When an infusion of tobacco was made use of instead of the empyreumatic oil, and injected into the rectum, the effects were different from any of the preceding, as the heart continued to contract, and was unifome found. in a state of extreme distension. Mr. Brodie is. however, of opinion, that the heart was not directly affected, but through the medium of the nervous system. For when the same