THE THORN-HEADED WORM. THE LEECHES 309 



faces in opposite directions, each having the part of male and female. 

 After the cross fertihzation is accompHshed there forms around the part 

 of the body where the sexual organs are located a clitellum which is a 

 sort of girdle secreting the capsules with which the eggs become sur- 

 rounded. The leeches then bury themselves in damp ground where the 

 eggs are deposited and incubation proceeds, this process occupying 

 about twenty-eight days. 



2. Hirudo medicinalis. The medicinalleech. Hirudinea (p. 307). — 

 This species is a little smaller than the horse leech. The dorsal surface 

 is darker than the ventral and is usually marked with six longitudinal 

 reddish stripes. The ventral surface is usually olive green and may 

 be more or less spotted. 



This leech was once extensively employed in medical practice for the 

 abstraction of blood. 



All of the domesticated animals and man are attacked by Hsemopis, 

 probably the horse most frequently. The leeches live in ponds and 

 springs where the animals are hkely to drink and are conveyed to the 

 mouth with the water. Those taken up are usually the young ones, 

 these keeping near the surface of the water, while the adults usually 

 lie in the mud at the bottom. Having thus gained access to the mucous 

 membranes, they fix upon the lips, cheeks, pharynx, or other parts of 

 the mouth. They may enter the nasal cavities through the nostrils 

 direct, or they may attach to the eyelids. While holding fast in these 

 positions by their oral and caudal suckers, the leeches lacerate the 

 mucous membrane with their cutting jaws and become gorged with 

 blood. They then detach and pass from their host, or they may attach 

 to another part of the mucous membrane and renew their feeding. 



The effect of the infestation will depend upon the number of leeches 

 present, and this is extremely variable. It is estimated that a single 

 leech when engorged will hold about eight cubic centimeters (two drams) 

 of blood. The host suffers an additional loss from the fact that there is 

 considerable hemorrhage from the wounds after the engorged leeches 

 have become detached. Heavy invasions, therefore, are capable of 

 bringing about considerable depletion with evidences of anaemia, as 

 paleness of visible mucous membranes, edemas, and emaciation. A 

 fatal asphyxia may develop from edema of the pharynx which may be 

 contributed to by the mechanical obstruction offered by the leeches in 

 this location. 



Treatment. — Where exploration of the mouth or nasal passages 

 reveals the presence of leeches, those which are accessible may be re- 

 moved by forceps or with the hand wrapped in a towel. Vinegar, or a 

 strong solution of common salt repeatedly applied with a view to causing 

 them to release their hold, is recommended by some, but the effective- 

 ness of such treatment can only apply to the leeches with which the liquid 



