ὀστεοκόλλα, in natural history, a white or ash-coloured sparry substance, in shape like a bone, and by some supposed to have the quality of uniting broken bones, on which account it is ordered in some plasters; a supposition we fear which is not warranted by experience. It is found in long, thick, and irregularly cylindric pieces, which are in general hollow, but are sometimes filled up with a marly earth, and sometimes contain within them the remains of a flake, round which the osteocolla had been formed; but though it is plain from thence that many pieces of osteocolla have been formed by incrustations round flakes, yet the greater number are not so, but are irregularly tubular, and appear to be formed of a flat cake, rolled up in a cylindric shape. The crusts of which these are composed do not form regular concentric circles round the internal cavity, as must have been the case had they been formed by incrustation. On the other hand, they plainly show that they were once so many thin strata, composing a flat surface, which has afterwards been rolled up, as one might do a paper three or four times doubled, into two, three, or more spiral lines; in which case, each single edge of the paper would be everywhere a regular point of a continued spiral line drawn from a given point; but they would by no means be so many detached concentric circles. The osteocolla is found of different sizes, from that of a crow-quill to the thickness of a man's arm. It is composed of sand and earth, which may be separated by washing the powdered osteocolla with water, and is found, both in digging and in several brooks, in many parts of Germany, and elsewhere. It is called hammoctous in many parts of Germany. It has this name in these places from its always growing in sand, never in clay, or any solid soil, nor even in gravel. Where a piece of it anywhere appears on the surface, they dig down for it, and find the branches run ten or twelve feet deep. They usually run straight down, but sometimes they are found spreading into many parts near the surface, as if it were a subterranean tree, whose main stem began at 12 feet depth, and thence grew up in a branched manner till met by the open air. The main trunk is usually as thick as a man's leg, and the branches that grow out from it are thickest near the trunk, and thinner as they separate from it. The thinnest are about the size of a man's finger. The people employed to collect it, when they cannot find any mark of it on the surface, search after the specks of white or little lumps of whitish soft matter, which they find lying in various parts on the top of the sand. These always lead them either to a bed of perfect osteocolla, or to some in the formation. If they miss of it, they still find a substance like rotten wood; which, when traced in its course, is found to proceed from a main trunk, at the depth of that of the osteocolla, and to spread itself into branches in the same manner. The diggers call this substance the flower of osteocolla or hammocteus.

The osteocolla found in the earth is at first soft and ductile; but in half an hour's time, if exposed to the air, it becomes as hard as we find it in the shops. The method to take up a perfect piece for a specimen is to open the ground, clear away the sand, and leave it so for an hour or thereabouts; in this time it will harden, and may be taken out whole. It is certain, that the osteocolla is produced at this time; for if a pit be cleared of it, there will more grow there in a year or two, only it will be softer, and will not harden so easily in the air as the other. What the rotten substance resembling the decayed branches of trees is, we cannot determine, unless it really be such; but the opinion of the common people, that it is the root of something, is absurd, because its thickest part always lies at the greatest depth, and the branches all run upwards. The osteocolla is a marly spar, which concretions round this matter; but what it is that determines it to concrete nowhere on the same ground but about these branches, it is difficult to say. The rottenness of this substance, which forms the basis of the osteocolla, renders it very liable to moulder and fall away; and hence it is that we usually see the osteocolla hollow. Sometimes it is found solid; but in this case there will be found to have been a vegetable matter serving as its basis, and instead of one branch, it will be found in this case to have concreted about a number of fibres, the remains of which will be found in it on a close examination. See Philol. Trans. n° 39.