LEECHES 



suction bulb pharynx or throat cavity (Fig. ii6). When a 

 blood-sucking leech finds a satisfying skin surface it attaches 

 its hind sucker and swings its head end about, exploring the 

 region. If possible it selects a spot where the skin is broken 

 or is particularly well supplied with blood. It then presses 

 down its anterior sucker, pushes its three jaws into the flesh 

 and makes a wound which is at first perfectly painless, but 

 ma}' later itch intensely. As the jaws enter the flesh, a small 

 amount of hirudin, the leech's saliva, pours into the wound and 

 mixes with the blood. Hirudin acts precisely like mosquito 

 saliva, preventing coagulation of the blood and keeping it thin 

 so that it can be easily sucked up. Like a mosquito bite the 

 leech bite will itch worse if the leech is removed soon after it 

 makes the wound ; but there will be almost no itching if it can 

 keep on sucking and finishes its meal. During the first part 

 of the meal the irritating hirudin fills the wound, but near the 

 completion it has been sucked out. An American medicinal 

 leech will take about two and a half times its own weight in 

 blood, which amounts to about half an ounce. This is possi- 

 ble because the fluid part of the blood is drawn off through the 

 kidneys of the leech even while it continues to suck from the 

 wound. Leeches produce some good preservative for their 

 food for it will keep in their stomachs not used up for nearly a 

 year. They have been kept in aquaria without food for fifteen 

 months. Leech bites are not dangerous to human beings ex- 

 cept through accidental infection of the wound, or in the rare 

 case of a "natural blee^der, " suffering from haemophilia, when 

 persistent hemorrhage will follow the bite. Leeches often 

 attack frogs and turtles in such numbers that they literally 

 suck the life blood out of them but painted turtles carry 

 three or four of them without seeming to feel any ill effects. 



Habitat. — Leeches abound in ponds, especially those of the 

 northern states; a few live on stones and boards in swift 

 streams, but most of them prefer quiet water. Sluggish ditches 

 swarm with them. The writer attended a country school near 



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