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haps than that all operations of art are exceeded by it. No chymical election, no chymical analysis or resolution of a substance into its constituent parts, no mechanical sifting or division, that we are acquainted with, in perfection or variety come up to animal secretion. Nevertheless, the apparatus and process are obscure; not to say absolutely concealed from our inquiries. In a few, and only a few instances, we can discern a little of the constitution of a gland. In the kidneys of large animals, we can trace the emulgent artery dividing itself into an infinite number of branches; their extremities
everywhere communicating with little round bodies, in the substance of which bodies, the secret of the machinery seems to reside, for there the change is made. We can discern pipes laid from these round bodies towards the pelvis, which is a bason within the solid of the kidney. We can discern these pipes joining and collecting together into larger pipes; and, when so collected, ending in innumerable papilla, through which the secreted Auid is continually oozing into its receptacle. This is all we know of the mechanism of a gland, even in the case in which it seems most capable of being investigated. Yet to pronounce that we know nothing of animal
secretion, or nothing satisfactorily, and with
which we want, that of evincing
Now supposing, or admitting, that we know nothing of the proper
internal constitution of a gland, or of the mode of its acting upon the blood; then our situation is precisely like that of an unmechanical lookeron, who stands by a stocking-loom, a cornmill, a carding-machine, or a threshing-machine, at work, the fabric and mechanism of
which, as well as all that passes within, is hidden from his sight by the outside case ; or, if seen, would be too complicated for his uninformed, uninstructed understanding to comprehend. And what is that situation? This spectator, ignoránt as he is, sees at one end a material enter the machine, as unground grain the mill, raw cotton the carding-machine, sheaves of unthreshed corn the threshing-machine ; and, when he casts his eye to the other end of the apparatus, he sees the material issuing from it in a new state ; and, what is more, in a state manifestly adapted to future uses ; the grain in meal fit for the making of bread, the wool in rovings ready for spinning into threads, the sheaf in corn dressed for the mill. Is it necessary that this man, in order to be convinced that design, that intention, that contrivance has been employed about the machine, should be allowed to pull it to pieces ; should be enabled to examine the parts separately ; explore their action upon one another, or their operation, whether simultaneous or successive, upon the material which is presented to them? He may long to do this to gratify his curiosity; he may desire to do it to improve his theoretic knowledge; or he may have a more substantial reason for requesting it, if he happen, instead
OF MECHANICAL ARRANGEMENT IN THE HUMAN FRAME.
We proceed, therefore, to propose certain examples taken out of this class ; making choice of such as, amongst those which have come to our knowledge, appear to be the most striking, and the best understood; but obliged, perhaps, to postpone both these recommendations to a third ; that of the example being capable of explanation without plates, or figures, or technical language.
OF THE BONES.
I.--I challenge any man to produce, in the joints and pivots of the most complicated or the most flexible machine that was ever contrived, a construction more artificial, or more evidently artificial, than that which is seen in the vertebræ of the human neck. Two things were to be done. The head was to have the power of bending forward and backward, as in the act of nodding, stooping, looking upward or downward ; and, at the same time, of turning itself round upon the body to a certain extent, the qua
drant we will say, or rather, perhaps, a hundred-and-twenty degrees of a circle. For these two purposes, two distinct contrivances are employed: First, the head rests immediately upon the uppermost of the vertebræ,
, and is united to it by a hinge-joint; upon which joint the head plays freely forward and backward, as far either way as is necessary, or as the ligaments allow : which was the first thing required.—But then the rotatory motion is unprovided for: Therefore, secondly, to make the head' capable of this, a further mechanism is introduced ; not between the head and the uppermost bone of the neck, where the hinge is, but between that bone, and the bone next underneath it. It is a mechanism resembling a tenon and mortice. This second, or uppermost bone but one, has what anatomists call a process, viz. a projection, somewhat similar, in size and shape, to a tooth ; which tooth, entering a corresponding hole or socket in the bone above it, forms a pivot or axle, upon which that
bone, together with the head which it supports, turns freely in a circle ; and as far in the circle as the attached muscles permit the head to turn. Thus are both motions perfect, without interfering with each other. When we nod the head, we use the hinge-joint, which