SANGUISUGA. 



through the water, but keeps an aerial stratum in close con- 

 tact with their respiring surface. When present in a limited 

 degree, this mucous secretion is highly serviceable to them ; in 

 excess it is destructive. It is impossible for them to diminish 

 *it when it has accumulated, or to denude themselves entirely 

 of their old skin in water only. They must have some resist- 

 ing body to creep over or through, in order to accomplish this 

 object. The most effectual method of preserving them appears 

 to be that recommended by Fee, which is as follows : " Into 

 a marble or stone trough, a layer of seven inches of a mixture 

 of moss turf and charcoal of wood is to be put, and some 

 small pebbles placed above it. At one extremity of the trough, 

 and midway between the bottom and the top, place a thin 

 plate of marble, pierced with numerous small holes, upon 

 which there should rest a stratum of moss or portions of the 

 Equisetum palustre, or horse-tail, firmly compressed by a stra- 

 tum of pebbles. The trough to be replenished with water 

 only so high that the moss and pebbles should be but slightly 

 moistened. A cloth is to be kept over the mouth of the 

 trough. This is imitating as near as possible their natural 

 condition, and the charcoal not only aids in keeping the water 

 sweet, but appears to prevent the leeches being attacked by 

 parasitic animals, to which they are very liable.^ The water 

 should be changed about once a week, and more frequently 

 in warm weather." To judge of the vast number of leeches 

 that are required for medical use, and of the great impor- 

 tance it is to ascertain the best method of preserving them, it 

 is only necessary to state, that four only of the principal deal- 

 ers in London import between seven and eight millions 

 annually. 



CHEMICAL AND MEDICAL PROPERTIES AND USES. 



LEECHES derive their principal interest from the use that is 

 made of them as a remedial agent; but it should be observed 

 that there are only two species so employed, and these are 

 principally derived from the South of France, Sweden, Poland, 

 and Hungary. It is common for the leech-dealers to drive 

 horses and cows into the ponds, that the leeches may fatten 

 and propagate more abundantly by sucking their blood. 

 Children are also employed to catch them by the hand, and 

 grown persons wade into the shallow waters in the spring of 

 the year, and catch the leeches that adhere to their naked 



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