DEVELOPMENT OF GUINEA- WORM 127 



to improve on this method by killing the worm by injection 

 of various substances; solution of perchloride of mercury, 

 i in 1,000, is that most commonly used. The worm thus 

 killed can often be readily extracted. Hot fomentations 

 relieve the pain and reduce the swelling ; boracic acid 

 fomentations are those most commonly used. 



Excision of the worm is difficult and should not be 

 attempted. Very extensive incisions are required and a 

 great part of the worm may not be superficial. If the 

 worm is broken it may be advisable to slit -up the sinus 

 and try to find the broken end, and by traction on this 

 the worm may be extracted in the usual manner. 

 Abscesses, if they form, and general cellulitis must be 

 treated in accordance with general surgical principles. 



Etiology. In the case of this worm the manner in 

 which the larvae are discharged clearly indicates that the 

 next stage of their existence is passed in water. In water, 

 however, though at first active they only live for a few 

 days, less than a week, and undergo no development. 

 Experiments on monkeys have not given any proof that 

 such larvae, if swallowed, will infect them. 



An intermediate host is required. Fedschenko showed 

 that they were capable of entering the body of a small 

 fresh-water crustacean, a cyclops, and that in this animal 

 the larvae cast their sheaths and become quiescent. 

 This first ecdysis, according to Leiper, in West Africa 

 occurs about the eighth day ; in a colder climate, as in 

 England, probably with a different cyclops, Manson found 

 it to occur in the sixth week. A second ecdysis occurs 

 two days later, and internal development is continued up 

 to the second to fifth week in West Africa. No further 

 changes occur, the larva appearing to have reached its 

 final development in its crustacean host. It does not 

 naturally leave its host, and even if the cyclops dies these 

 Guinea-worm larvae remain in it. 



Many observers had discussed the question as to the 

 further fate of the larvae, some holding that the embryos 

 penetrated the skin of man and then further developed, so 

 that infection of man took place whilst he was bathing. 



