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 136 the description which Mr. Douglas gives of the constituency of the crust. He is well worth hearing twice:—

‘If the crust is closely examined with a microscope, its structure will be found to consist of a number of bristle-like fibres standing on end, but bearing diagonally towards the ground. From the particular longitudinal construction of the fibres, it follows that they will bear a great amount of weight, so long as they are kept in their natural state. The crust so viewed resembles a number of small tubes, bound together by a hardened glue-like substance. Whoever has seen a mitrailleuse gun, with its numerous barrels all soldered together, can form a very good idea of the crust, especially if they were likewise to imagine the tubes to be filled with a thick fluid the use of which is to nourish and preserve them.’

We have already seen that the driving of nails, in any form, must both lacerate and close up, either totally or partially, these delicate tubular fibres containing the fluid which gives life; but when we come to consider that in driving them askant from right to left the farrier is causing a double amount of laceration, we shall easily comprehend that the further the disease spreads, the more he helps it to do so. Well may Mr. Lupton say:—‘Farriers ought to go through a course of instruction previously to being allowed to operate upon structures the anatomy, physiology, and economic uses of which they have never studied, and, consequently, never understood.’