Hence we must crowd out the weeds as much as possible by useful plants which will bring something towards the cost of their removal; and as that return from perishable greenstuff is dependent upon its immediate sale or consumption on the farm, the manager must cast about for demands for his abundant supply; but as both the sunshine (in this climate) and markets are very capricious factors in the problem, he has no easy task always to make both ends meet. Theoretically the town which yields the sewage ought to provide an abundant demand, but in practice it can rarely be depended upon, Edinburgh being the only exception, where the Craigentinny sewage meadows are rented at a very high figure by the cow-keepers of a city situated in the heart of an arable district. [Sidenote: Alternative destinations for vegetation thus removed. Milk (everywhere in demand) or a destructor furnace.] Fortunately, however, there is always an unlimited demand for milk, and if he has the means of keeping a herd of cows on the farm, or can arrange with a neighbouring cow-keeper to take all the grass and roots he can supply at a low rate, it is about the best course a manager can adopt. If he maintains a herd of cows, tied up in good, well ventilated stables, and has them daily brushed and groomed like horses, they require no exercise and produce milk in perfection for an average period of fifteen months from date of purchase after their third or fourth calving. Such a herd will consume rye-grass carted from the field from April to November, and mangolds, kohl-rabi, and rye-grass hay during the winter, thus securing a uniform demand for produce of the sewage land throughout the year, and such cows will only require a little cotton cake and oat straw bedding (of which latter they eat a good deal) to fit them for sale to the butcher as soon as they become dry. The advantage of such a steady demand is so great when rye-grass and mangolds, etc., are indicated as the main crops of the farm, owing to the large volume of sewage per acre, that the system of cow-keeping is forced upon managers, however reluctant their sanitary authorities may be to provide the necessary working capital, unless they can find a reliable contractor to receive at a fixed price any quantity of grass and roots the authority may grow and deliver. [Sidenote: Permanent pasture grazed and for hay available in certain cases.] When a town has more land in proportion to its sewage, permanent pasture may take the place of Italian rye-grass, and, with proper precautions, a part of the permanent pasture may be grazed; but the saving of labour, thus supposed to result from letting animals bite and carry their food, is expended in making up, in a necessarily imperfect manner, the carriers trodden in by the cattle. [Sidenote: Importance of neat tidy contour carriers, correctly levelled.]