The health and " biting " propensities of the Sanguisuga depend upon a number of circumstances, some of which are rather obscure, but it may be stated in general terms that the absence of decaying animal matter, and of too great an excess of lime-salts, are points which should be aimed at most particularly. Sudden changes of temperature are also detrimental to leeches, which should, as may be inferred from the preceding remarks, be kept in soft water of good quality frequently renewed, provided it is not too pure to afford them nutriment. They are peculiarly sensitive to electrical influences; many confined in the usual small receptacles will sicken and die, apparently "quite unaccountably," but really from the effects of that electro-inductive condition existing before a thunderstorm, and popularly known as " thunder in the air." If the usual leech-vase or barrel, say of glass or china, be put into direct conductive communication with the earth by means of a stout metallic chain dipping into the water and connected by its other extremity to, say, the gas- or water-pipes of a house, fewer leeches in summer will die than if this precaution is not taken.
When kept in the usual rather small vessels, the water should be, if possible, rain-water of good quality, renewed every 8 or 10 days with fresh water of the same temperature* as that in the leech vase itself. Dust must be excluded from the vessel by a covering of fine gauze, and the bottom should be occupied by a layer of clean fine gravel or coarse sand, to which has been added a few lumps of well-burnt oak or pine-wood charcoal. The whole of this bottom layer should be renewed within 6 to 8 or 10 weeks, according to the time of year. A little pure " crystallized" binoxide of manganese in the granular condition, and carefully freed from fine powder by sifting, is often of great assistance in keeping the water in a wholesome condition. Towards the same end also, a few growing plants of the Vallineris spinalis will powerfully contribute; but perhaps the most efficient factor in this direction, wherever it can be applied, is an arrangement for keeping the water slightly agitated and at the same time well aerated. This object can be readily attained by any simple "aspirator," whereby a slow current of water forces air down a small glass tube turning up under the surface of the fluid in the leech receptacle.
In the end of this tube a small transverse section of dry cane should be cemented, so that the air emitted is distributed in minute bubbles. (Burgoyne's Monthly.)
* As far as possible this should be kept within the limits 65° to 76° F. (13° to 24° C.)
(2) Complaints are frequently heard of the inability of chemists to keep their leeches in health for any length of time. I have avoided the advertised leech aquariums and the like, and have for years kept leeches in perfect health by the following simple plan: - I got a 7-lb. ointment jar, made of glazed white earthenware, and put my leeches into it. Then, instead of replacing the top, I covered the jar with white muslin, and tied it round tightly. The water was never allowed to go unchanged more than a week; and by these simple means I have been able to keep all the leeches alive for months, even during the hottest weather, when the mortality amongst them is usually very great. (E. F. Cherry.)