SANGUISUGA. 



proceed from taking off the -leech by force when it is sucking, 

 thus causing the teeth to separate from the animal and remain 

 in the wound. 



The leech should therefore always be permitted to drop off 

 spontaneously; and when it drops off, it should be thrown 

 into water slightly salted, till it disgorges the blood, after 

 which it should be thrown into clean water. It is curious that 

 the circumstance of the leech dropping off when it is gorged 

 has never suggested the question, What causes the leech to 

 drop off? The usual reply to this question is, that the leech 

 has had sufficient ; or that it drops off from the uneasiness of 

 distention. This, however, is not the fact ; it drops because 

 it falls into a state of asphyxia, from want of respiration, and 

 this is founded upon the following grounds. The respiratory 

 organs of the leech are a number of vesicles in immediate 

 contact with the lateral longitudinal vessels, small twigs of 

 which communicate with these vesicles, to submit the blood 

 to the action of the air, which is admitted by stigmata or spi- 

 racles, which are arranged on each side of the under surface 

 of the animal between every fifth ring. As the vesicles con- 

 tain a whitish fluid, they are supposed not to be respiratory 

 organs ; that they are, however, breathing organs, is proved, 

 for on closing these pores with viscid oil, the leech dies in a 

 few days. Now, these vesicles communicate with the air; 

 and although the leech can live for some days under oil, and 

 in the exhausted receiver of an air-pump, yet, from an experi- 

 ment made by Dr. Edwards, it is evident that the leech re- 

 spires and consumes the oxygenous portion of the air ; and it 

 may be inferred that the animal, by filling these vesicles with 

 air, can exist for some days without a fresh supply ; but it by 

 no means follows that they can exist if these vesicles be en- 

 tirely emptied. It is therefore considered that the animal 

 continues capable of exerting the function of sucking as long 

 as these vesicles contain a sufficiency of air for the respiration 

 to be carried on ; but as the body becomes greatly distended 

 with blood, the cavities of these vesicles are obliterated ; no 

 respiration can consequently take place ; and, as in animals 

 that breathe by lungs, asphyxia occurs as soon as air ceases 

 to be retained in these vesicles, and the muscular energy 

 depending on volition being no longer exerted, the leech drops 

 off. If it be true that, when the tail is punctured or is cut 

 off, the leech continues to suck, it is because no asphyxia 



14 



