Many kinds of tiles and pipes have been tried, but the cylindrical form is most used. At one time, a bore in the tile of an inch in diameter was thought sufficient, but 2-in. tiles are now preferred. They tire usually made about 15 in. in length. The con tinuity of the drain is maintained completely by collars, which should always be used as a means for securing efficiency and permanency. In soft mossy or clayey subsoils, semi-cylindrical tiles called muggs have been laid, with the bend up, on lath. This is expensive, but is necessary in some cases.
Much discussion has taken place in regard to the proper depth of drains, as well as the distance at which they should be placed. Mr. Smith at first advocated the making of drains from 2} to 3 ft. deep, and at intervals of from 10 to 40 ft., according to the nature of the land. Experience, however, has been gradually favoring deeper drains, at wider intervals. Even on the most tenacious soils with subsoils of till, few LOW think of having drains less than 3 ft. in depth, though the distance apart should not in many cases be more than from 15 to 18 feet. The depth, however, depends greatly on the soil-34 and 4 ft., with the leader drains 6 in. more, are common dimensions. In mossy land the depth has sometimes to be 7 feet. The width between drains depends on the wetness of the land and the character of the subsoil.
The mere tenacity of clays is not the element which determines the depth of drains, or the distance at which they should be placed apart. It is now well understood that the success of draining by pipes depends upon the fissures which are produced in the subsoil by the droughts of summer never entirely closing up; and thus minute channels are formed, which lead the water into the drains, As the properties of clays become better understood and classified, practical men come to be more at one in regard to this important point connected with the economy of drainage.
The principal advantages of D. are, the deepening of the staple soil, and rendering it more friable, so that a superfluity of water, which would cause the formation of those chemical compounds that are found in stagnant water, is prevented. The greater depth of mold, and more perfect culture, render the soil more absorbent of moisture in dry weather. As crops can usually be sown sooner on drained lands, they also ripen earlier, and produce more abundantly. In short, while drained land obtains a greater capacity for moisture and manure, it imparts to plants greater capabilities for economically work ing up the materials which they find in the soil and atmosphere, seeing they are main tained in the most healthy conditions of growth.
D. in its various forms has, as is well known, not only improved the fertility and value of land in Scotland, but materially changed the aspect and climate of the country.
Mosses and wet rushy lands have been transformed into dry and productive fields, while by the removal of all superfluous pools, the air is freed from those hovering vapors which are injurious to general amenity and salubrity. To the farmer, the more imme diate advantage of D. consists in that rapid running off of the water which falls as rain, so as to admit of working lands without any undue delay, while natural springs and dampness, from whatever source arising, are also run away with wonderful success. In short, subsoil D. has been perhaps the most valuable improvement connected with British agriculture.
in surgery, are a recent hut important addition to the surgical appliances for which this profession is indebted to a distinguished French surgeon, M. Chassaignac. They are composed of India-rubber, from ith to Ith in. in diameter, per forated with numerous holes, and of various lengths. They are especially useful in chronic abscesses (which it may be unadvisable to empty at once) and empyema (q.v.), but also in large wounds, such as those made by amputation, and in all cases where there is apt to be a deep accumulation of discharge. They are introduced in such a manner that one end is on a level with, or projects above the skin; the other is in communica tion with the seat of discharge; and by allowing that discharge constantly to escape from the external wound, they diminish both chemical irritation from putrid accumu lation, and mechanical irritation from pressure. Like all new inventions, it has its advocates and opponents. Thus, while sir William Paget, in his article "Sinus and Fistula," in Holmes's System of Surgery, says that "d1,-..-kage, for which the perforated caoutchouc-tube of M. Chassaignac is a very happy invelition, is applicable to a great number of cases; but chiefly to those in which a sinus or incomplete fistula depends mainly on pus collecting at a level below or distant from the aperture of discharge, or more generally, when pus is apt to be retained."—Sir William Paget's surgical colleague at St. Bartholomew's hospital, in his article "Abscess," which immediately precedes that from which we have just quoted, objects to the drainage-tube on the grounds that, as a foreign body, it sets up irritation, and adds that "if a proper opening be made, there can be rarely any occasion for a drainage-tube; and however carefully it is inserted, it must of necessity inconvenience and distress the patient." Notwithstanding Mr. Coote's objections, drainage-tubes are now very generally used in surgical practice.