LEECH 529 



ANIMALS 



LEECH 



(Hirudo) 



Source, &C. Leeches are aquatic worms, and are bred in ponds for 

 medicinal use, chiefly in Germany (near Hanover) and in the south 

 of France (near Marseilles). Two varieties are official viz. the 

 speckled leech, Hirudo medicinalis, Linne, and the five striped or 

 Australian leech, Hirudo quinquestriata, Schmarda (Phylum Annelida, 

 Class Hirudinea, Order Gnathobdellida) ; they may be distinguished 

 by the ventral surface, which in the former is of a greenish 

 yellow colour, spotted with black, whilst in the latter it is not 

 spotted. 



Although the dorsal surface of the leech is marked with numerous 

 (about 100) annulations, the body is not divided into distinct segments. 

 It tapers towards each extremity, and is provided at each with a 

 sucking-disc by which it can attach itself to any object. The 

 anterior disc, which is smaller than the posterior, contains three jaws 

 radiating from a common centre ; each jaw is furnished with a number 

 of minute teeth, and resembles a portion of a circular saw. The 

 animal attaches itself by means of its anterior sucker to the skin, 

 which is thereby slightly raised ; the three jaws, by a saw-like 

 movement, produce three slits which unite to form the characteristic 

 triradiate cut, and the leech gorges itself with blood ; it then 

 relinquishes its hold, and drops from the skin. The blood which it 

 has drawn is so slowly digested that a single meal will last for several 

 months. 



Although the leech is hermaphrodite that is, both sexes are 

 united in the same individual it is incapable of self -fertilisation. It 

 reproduces itself by means of eggs, and the young require about five 

 years to arrive at maturity. 



The quantity of blood that a leech will draw is not large (from 

 4 to 8 c.c.), but the flow of blood from the cut is often continued for 

 some time ; this appears to be due partly at least to a substance, 

 hirudin, which is secreted by the salivary glands of the leech and in- 

 jected into the cut. The flow of blood can also be maintained by 

 fomentation. 



. Leeches are used to reduce inflammation by withdrawing 

 blood. Hirudin, which retards the coagulation of blood, has been 

 suggested for use in thrombosis and other conditions in which the 

 blood shows a disposition to clot too readily. 



34 



