HIRUDO MEDICINALIS Linnaeus 



Material. Live leeches may be bought in any pharmacy 

 and can be kept alive in an aquarium, without food, during many 

 months, or they may be allowed to suck the blood of frogs. 

 Two hours before the exercise the leeches should be placed in 

 10% alcohol with a few drops of chloroform. The alimentary 

 canal may be injected, though this is not essential. A red gela- 

 tine mass gives good results, but carmin suspended in a solution 

 of celloidin is preferable. The mass is allowed to harden by 

 placing the injected leech with the needle in 70% alcohol. 

 To prepare material for transverse sections the leech must be 

 stretched in a dissecting pan by means of two pins and fixed in 

 a mild fixing fluid such as Perenyi's. The best imbedding me- 

 dium is celloidin. Transverse sections of imbedded specimens 

 for study under the dissecting microscope should be cut with a 

 common razor to the thickness of one annulus. These sections 

 can be preserved indefinitely in alcohol. Thin sections may be 

 stained in haematoxylin and eosin or orange G. 



Descriptive Part 



The leech is a hermaphroditic segmented worm inhabiting 

 stagnant fresh-water pools of Europe and imported into this 

 country for medicinal purposes. The development of the leech 

 shows that it is composed of thirty-three l segments, a number 

 characteristic of all segmented worms of the Class Hirudinei. 



1 According to some investigators the head of the leech is composed of six 

 segments and the whole number of segments is therefore 34 and not 33. In 

 this case the segment with the male genital opening would be the eleventh 

 and the last visible segment the twenty-seventh, and not the twenty-sixth. 

 It is situated between the fourth and fifth pair of nephridiopores. 



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