Many of his remarks, as well as the ingenious suggestions with which they are interspersed, exemplify the caution with which he reasoned. In speaking of his experiments on leeches and tadpoles, many of which latter had become perfectly developed frogs, he says: "The experiments which I made on this plan (in vessels of distilled water, covered with linen) were made in the summer, when to prevent vegetation was impossible; and, on the other hand, when the vessels were covered over, even leeches died. In the winter, vegetation might cease; but then the torpid state of the animals would render the experiments inconclusive."
He reduced an equal number of eggs and chickens (at the time of incubation) to ashes; sometimes in crucibles, sometimes in retorts. On the ashes he poured some distilled water, and ascertained the salts (as lime, &c.) contained in them. In some experiments, the quantity of these found in the ashes of the chickens greatly exceeded that found in the ashes of the eggs. In other experiments, the quantities were equal.
In some of his experiments, after using the best chemical tests for detecting iron, lime, and the salts, and then washing the residue with distilled water, he burnt it in a crucible, and found more lime and iron; on which he makes the following remarks, which suggest what we apprehend, even at this time, is a very necessary caution:
"This circumstance proves to me that the substances found in the ashes of burnt animal matter do not formally exist in the mass before its destruction, but are only new distributions of the same ultimate particles which, under their former mode of arrangement, made the animal substance; but which, being driven asunder by the repulsive power of fire, are left at liberty to form other modifications of matter." Page 97. Just what happens when animal matter is burned, in the formation of ammonia, by the union of the nitrogen and hydrogen then set free.
He investigated, also, the question of how far the results of the decomposition of animal matter would be identical, if the analyses were conducted by heat, or by putrefactive decomposition. In this experiment, he selected blood; and he found that blood which had been allowed to putrify yielded _a much larger quantity_ of iron and lime.