The total excrements voided by a horse in a day have been calculated, according to the average of experiments by Boussingault and Hofmeister, at 28.11 lb., of which only 6.37 lb. consisted of dry matter.[151] These 28.11 lb. contained .18 lb. of nitrogen and .92 lb. of mineral matter. The amount of straw necessary to absorb this amount of excrement may be stated at from 4 to 6 lb. The amounts of nitrogen and mineral matter in 4 lb. of straw are .01 and .23 lb. respectively. The total amount of nitrogen and ash, therefore, in the farmyard manure produced by a horse in one day, would be .19 lb. nitrogen and 1.15 lb. mineral matter; or, if we take the larger quantity of straw, somewhat more. Taking these figures, we find that the amount of manure produced by a horse in a year will be from 11,720 to 12,450 lb. (_i.e._, from 5-1/4 to 5-1/2 tons),[152] containing from 69 to 73 lb. nitrogen, and from 420 to 460 lb. mineral matter.[153] A word or two may be of value regarding the treatment in the stable of horse-manure. The great object to be aimed at is the prevention of loss of valuable fertilising constituents. This loss may be due to two causes. It may be, in the first place, caused by drainage of the soluble matter of the manure; or secondly, it may be due to volatilisation of the volatile constituents. The first of these two sources of loss depends on the precautions taken in the way of providing a proper impervious flooring to the stable. This source of loss is extremely difficult to prevent, inasmuch as nearly all materials used for flooring absorb a certain percentage of urine. The judicious use of litter, however, will minimise this loss to within a trifling extent. Dr Heiden states that the amount of straw used as litter for the horse in Germany is from 4 to 6 lb. per day. The quantity should be regulated according to the percentage of water the excreta contain; the more watery excreta requiring naturally a larger quantity of litter. The most eminent authorities on this subject recommend that the amount of litter should equal one-fourth of the food in its natural state, or about one-third of its dry substance. The second source of loss, which is due to volatilisation of the volatile ingredients, may be largely prevented by the use of certain preservatives.