CHAPTER 2 



THE MEDICINAL LEECH, 

 HIRUDO MEDICINALIS 



He with a smile did then his words repeat: 



And said that, gathering leeches, far and wide 



He travelled ; stirring thus about his feet 



The waters of the pools where they abide. 



" Once I could meet with them on every side; 



But they have dwindled long by slow decay; 



Yet still I persevere, and find them where I may." 



WORDSWORTH, Resolution and Independence ^ 1802. 



1. Occurrence 



The medicinal leech feeds by sucking the blood of mammals or 

 occasionally of frogs, tadpoles and small fish (Blair, 1927). It is a 

 native of Europe and south and east Asia (Lukin, 1957) and has 

 been introduced into North America. In Britain it was once plenti- 

 ful, but in the last two hundred years has declined markedly, 

 possibly as a result of its extensive collection for medical use. It 

 was once thought to be extinct in Britain (Harding, 1910) but is 

 now known to be present in various relatively undeveloped areas 

 such as the New Forest, the Lake District, South Wales, Anglesey, 

 and Islay, Scotland. Its opportunities for obtaining blood from 

 mammalian hosts have been greatly reduced now that fords have 

 been replaced by bridges and cattle are watered at troughs rather 

 than natural ponds. 



2. External Characters 



A large specimen measures about 12 cm X 1*5 cm when fully 

 extended, although it may contract to less than half this length. 

 The shape of the body varies according to the amount of blood 



