They resemble in general appearance the breaking engines previously described; the roll, however, carries more knives, and it is usually let down much nearer to the bed-plate. In the case of fibrous substances, whose ultimate fibres are relatively short (see table, p. 39), it is only necessary to split up the filaments into their constituent fibres: esparto, straw, and wood are of this class. In the case of straw, the disintegration is for the most part accomplished in the boiling and bleaching processes, and therefore but little work devolves upon the beater. Esparto and wood require a certain amount of beating, but this should be regulated to the drawing asunder of the individual fibres, any cutting of the fibres being carefully avoided. This is accomplished by adjusting the distance of the roll from the bed-plate, so that by the friction of the fibres upon themselves, when passing over the plate, a kind of rubbing or “brushing” is produced. If a carefully-made paper of esparto or wood be examined by the microscope, it will be found that the majority of the fibres preserve the pointed or slightly rounded ends {118} characteristic of bast cells. On the other hand, it is obvious that cotton, whose ultimate fibres have a length of 20 to 40 mm., and flax (25–30 mm.), with other similar fibres, will require to be broken up into short fragments in order to develop to the fullest the felting property of the pulp. Not only are the fibres reduced to the most favourable dimensions, but in cotton and linen a further contributory advantage accrues; for on account of the internal structure of the ultimate fibres they tend to split up at the point of rupture into a number of fibrillæ, which, in the case of cotton, take the form of a network; and in case of linen, are seen as a bundle of distinct fibres parallel to and continuous with the fibre. This gives to ends of the fragments a ragged contour, which has considerable influence on the felting power of the pulp, and therefore on the strength of the paper into which it is made. With these fibres, therefore, the “cutting” as distinguished from the “breaking” action should be avoided as much as possible, otherwise the effect described above will not be produced, and the fibres will show instead a clean cut. The appearance shown by cotton and linen pulp, when thoroughly “beaten” and ready to be made into paper, is given in the frontispiece, which is taken from the author’s micro-photographs.