84 BEVIEW — TROPICAL MEDICINE, ETC. 



Guinea He points out tliat these theories have become discredited, and gives further 



Worm — experimental and literary evidence in favour of their being discarded. The embryos cannot 



ointiiiuol infect man by the skin or mouth or undergo further development in water. His own 

 observations on the vitality of the embryos in water show that the usual period of survival 

 was three days, though some survived till the sixth day. In mud they lived a day or two 

 longer, probably because in this medium they move more slowly and are consequently 

 exhausted. Although provided with a mouth and digestive tract they are still unable to 

 obtain food for themselves. 



ii. Those in which an intermediate host is considered essential fur the development of tlu^ larv.-i in order 

 that it may become iitted to re-infect mnu. 



(d) The only, and in itself suiBcient, host being Cyclops. 



(c) A second, and at present unknown, intermediate host being necessary to continue and complete 

 the changes begun in cyclops. 



Leiper, in his experiments in Nigeria, found that, of all the organisms in the ponds, 

 Cyclops alone was capable of infection, and he believes that the mode of entry of the 

 embryo is not through the integument of the cyclops, as usually taught, but by way of the 

 intestine. As regards the completion of metamorpliosis, ho found tliat the striated cuticle 

 of the embryo was cast generally on the eighth day. The larva which emerged lost, two 

 days later, a very delicate enveloping pellicle, and from that time onwards underwent no 

 further ecdysis. The subsequent changes were confined to the differentiation of internal 

 structures, the larva apparently becoming mature in the fifth week. These observations 

 differ from those hitherto accepted. 



Leiper also noted that the larvae showed no disposition to leave the cyclops and become 

 free-swimming, evidence that infection of man does not occur by the skin. As time went 

 on the larvae became more quiescent, and when the cyclops died the larvae were found dead 

 in its interior. 



As regards the way in which they leave their host, Leiper^ refers to his pi'evious work, 

 in which he demonstrated the action of a 0-2 per cent, solution of hydrochloric acid in 

 killing the cyclops and rousing the larvae to such activity that they speedily escaped by the 

 mouth, anus, genital opening, or a breach in the cuticle of the cyclops, and swam about 

 freely in the fluid. 



The later work has consisted in feeding a monkey on bananas containing cyclops 

 which had been infected for five weeks, and which had in them apparently mature larvae. 

 Six months later a careful post-mortem examination of the monkey revealed the presence in 

 the connective tissues of five filarite, which possessed the anatomical characteristics of 

 Filaria inedinejisis. There were three unimpregnated and obviously immature females about 

 30 mm. long, and two remarkably small males (22 mm.), which were obtained one from the 

 psoas muscle and the other from the connective tissue behind the oesophagus. These 

 results (says Leiper) point strongly to the truth of the theory that infection of man takes 

 place from the drinking of water containing infected cyclops. The suggestion that a second 

 intermediary host is necessary for the complete development of the guinea worm larva is 

 disposed of by the fact that this is actually attained in cyclops. 



He comments upon the importance of the discovery of the male and immature female 

 forms in the connective tissue, showing that the guinea worm thus comes into line with 

 what we know of the after-development of other filariaj. 



He thinks that Geotropism (tendency to grow downwards towards the earth) affords a 

 rational explanation of the remarkable distribution of the parasite in man. 



An important fact to which attention is drawn is that the embryos are immediately 

 killed if dried by natural evaporation, and they cannot be revived by the re-addition of water. 



A review is given of the conditions essential for the completion of the life-cycle of the 

 parasite, as follows : — 



The young must be discharged directly into fresh water soon after the parent worm h.as succeeded in creating 

 a break in the overlying ^kiu and before the wound has become markedly septic. The embryos must find a cyclops 

 within a few days. They must, moreover, succeed in entering its body cavity. Five weeks later they will have 

 developed into mature larvse. These must, thereafter, be taken into the human stomach, and having been set free 



• Leiper, R. T. (January 6th, 1906), "The Influence of Acid on Guinea Worm Larva encysted in Cyclops." 

 British Medical Journal, p. 19, Vol. \. 



