These sponges, nests, or cells, are attached to some solid body in the sea. Some kinds are fixed to rocks; others, as those I am speaking of, are fastened to heaps of sand, or to pieces of petrified matter, and even upon sandy bottoms; and the sea putting in motion the sand, and the little parcels of broken shells, forces them into the holes of the sponge: there the sand binds and mixes with mucilaginous juice, and never is loosed from it but when the sponge is well dried, or with the mucilage when putrified, or in powder; and yet some part will remain, which it is very difficult to take out from the twisted canals, especially in those sponges of the _tragos_ kind, so hard to cleanse. In a word, the blood or humours, which the ancients have observed, is no other than the mucilage or juice of the substance of these worms. Dated at Guadaloupe, 1 March, 1757. LXXIX. _Account of an Experiment, by which it appears, that Salt of Steel does not enter the Lacteal Vessels; with Remarks. In a Letter to the Rev._ Tho. Birch, _D. D. Secr. R. S. By_ Edward Wright, _M. D._ [Read Mar. 2, 1758.] SIR, THO’ iron is universally allowed to be one of the most powerful medicines now in use, yet many physicians observing, that the _fæces_ of patients, who used it either in a metallic or saline form, were tinged of a black colour, have been led to think, that, in a metallic state, it could not be reduced into particles fine enough to be received by the lacteal vessels; and if taken in a saline form, that it underwent a precipitation in the intestines, by which, being reduced to an earth or calx, it was in like manner rendered incapable of making its way into the blood. But the accurate experiments, with which Signor Menghini has favoured the public in the Memoirs of the Bononian Academy[34], sufficiently prove, that the ore and filings of iron, finely levigated, enter the blood in considerable quantity; as does also the _crocus_, _calx_, or earthy part of the metal, tho’ in less proportion than the two former, which were found to act with a violent _stimulus_ on the vessels, and to have dissolved and broke the _crasis_ of the blood of different animals, that had used them for some weeks in large doses mixed with their ordinary food. Tho’ it must be allowed, that these experiments are very curious, yet the subject seems to require a further inquiry, viz. _Whether iron is capable of entering the blood in a state of solution, or under a saline form_: for, from the violent _stimulus_, as well as from the dissolution of the blood, and other symptoms brought on by the use of the ore and filings, these substances (not being properly dissolved) appear to have acted in a manner so grossly mechanical, that, whatever Signor Menghini may think, very little is to be concluded from them, with regard to the action of iron on the human body, in such cases, as indicate its use, and where a rational physician would think proper to prescribe it as a medicine.