204 



ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



that portion of the body. The head of the worm bores towards the 

 surface and the epidermis rises up over it as a blister which presently 

 bursts, forming a small ulcer with the opening of the burrow in which 

 the worm lies in its centre. 



If now the ulcer comes into contact with cold fresh water the worm 

 contracts the muscular wall of its body and forces out a portion of its 

 uterus, which immediately bursts and exudes a drop of milky-looking 

 fluid, containing myriads of young worms coiled up in spiral form. 

 These larvae measure usually from -5 mm. to -75 mm. in length, are 



somewhat flattened, and have the hinder 

 end of the body drawn out into a fine 

 point. 



Contact with the water rouses the 

 larvae to activity. They uncoil themselves 

 and swim away rapidly. They are capable 

 of remaining alive for a period of up to 

 three days but do not proceed with their 

 development unless within that period they 

 find their way into the interior of a small 

 fresh-water crustacean — Cyclops (Fig. 94). 

 According to the older accounts the young 

 Dracunculus bores its way into the body 

 of the Cyclops between the hard plates 

 covering its abdomen. More recent ob- 

 servers State that it has to be swallowed 

 by the Cyclops, and that within a period 

 of from 6 to 24 hours it has bored its way 

 through the wall of the alimentary canal 

 and taken up its position in the blood- 

 spaces (haemocoele) of the crustacean. 

 Within the body of the Cyclops various changes in detail take place 

 and after about five weeks the larva is ready for transference to its 

 mammalian host. This takes place apparently by the infected Cyclops 

 being swallowed in drinking water. 



The obvious precaution to take against infection with Dracunculus 

 is to see that all drinking water is either filtered, heated, or otherwise 

 treated, so as to destroy the Cyclops. Where the individual is already 

 infected the superficial ulcer should be douched with cold water at in- 

 tervals until — after 2 to 3 weeks — the uterus is completely emptied. The 

 body of the worm may then slowly be drawn out by winding it round 

 a stick, an inch or two at a time, or it may be killed in situ by injecting 



Fig. 94. 



Cyclops, 9 containing two 

 Dracunculus larvae (D). 



