The type of machine often used, however, is shown in Figure 18; the working part is a long spindle fitted with helical knives. The advantages of this machine are its large output and its use for other operations by simply changing the working roller. The blades must be blunt for dehairing, but sharpened blades are needed for fleshing. If hides intended for sole leather are being dehaired, the short hairs which are not removed by the dehairing knife are carefully scraped off with a sharp knife. Other kinds of hides and skins are freed from short hairs in a later operation. When the hides are dehaired, they are sometimes submitted at once to the next operation of fleshing, which, as its name implies, consists in removing loose flesh and fat from the "flesh" side, that is, the side near the carcase. The extent to which this operation is carried out depends on the quality of the finished leather. Naturally, the more flesh left on the greater the weight, particularly as loose flesh will absorb a large quantity of tannin, and, unfortunately, of adulterants which are frequently used for weighting common leathers. The flesh ought to be removed in all cases, for the loose flesh forms very poor and spongy leather. Where hides and skins are tanned and then dried for sale to leather dressers and finishers, there is often the tendency to leave far too much loose flesh on them, with the object of producing as much weight of leather as possible. From the point of view of economy, this is a mistake, for the loose flesh must be removed during the dressing process, whereas, if it had been taken off at first, both material and time would have been saved in the process of tanning. If the fleshing is not done directly after dehairing, the hides or skins should be placed in a weak lime liquor, and this method is to be recommended. The great point to be observed is to keep the limed hides, both before and after dehairing, away from contact with the air, as the chemical action of the carbonic acid on lime results in the formation of chalk, which tends to harden the hides and to roughen the grain, so that it is likely to be scratched in later operations. Where the hides are intended for sole leather, and not treated with an acid before entering the tanning liquors, the presence of chalk would lead to an uneven colouring of the leather. [Illustration: FIG. 19 FLESHING KNIFE]