"Great" industry demanded the division--even the disintegration--of labour. The product, before it is finished, passes through the hands of various craft groups. It undergoes a series of processes which follow one another and are interdependent, and of which each is carried out by specially trained workers. This was the case in the manufacture of wool from the thirteenth century. The wool had to be washed, beaten, carded, combed, oiled, spun, woven, fulled; then the cloth had to be stretched, dyed, dressed, and folded. It is a well-known fact that if each class of work is entrusted to a special class of workers, manufacture costs less both in money and in time. But it must be added that this disintegration of the whole process into a succession of operations leads straight to the mechanical system.[101] The simple and monotonous tasks performed under this system of subdivision by the different classes of workers owe their automatic and half-mechanical character to the uniformity of the movements they demand. It needed very little to complete the technical revolution already begun and to make hands of wood or metal accomplish what had been done by human hands. A machine may be described as a more or less complicate engine, which, by means of an animate or inanimate motive force, executes movements which hitherto have been performed by the human hand. The weaving loom and the spinning wheel were already rudimentary machines. The Middle Ages knew, under the name of "mills," more complicate appliances, of which many date from the Alexandrine period, which was to Graeco-Roman antiquity what the nineteenth century is to modern times--the era of science and machinery. Water- or wind-mills, mills for grinding flour, for crushing nuts or olives, for raising water; iron mills; mills for fulling cloth, for making paper, sugar, silk stuffs--all these expensive appliances were in use, and gradually spread over Europe during the period which brought to a close and immediately followed the Middle Ages. Thus old industries changed their method, and new industries were from the start modelled on the new system.