310 THE SPREAD OF INTESTINAL WORMS BY FLIES 



which had been fed upon honey with whieli the eggs of the tape- 

 worm had been mixed. 



The most complete and valuable series of experiments on the 

 dispersal of the eggs of parasitic worms of flies has been carried 

 out by Nicoll (1911) in connection with the Local Government 

 Board enquiry. He recognised the isolated nature of the work of 

 previous investigators, and while the account of his experiments is 

 described as being of a preliininaiy character it contains many 

 results and observations of considerable value. Ten species of 

 parasitic worms were experimented with, namely, the tape-worms. 

 Taenia serrata, T. marginata and Dipylidium caninum from the 

 dog, Hymenolepis diminuta from the rat, Moniezia expa^isa from 

 the ox, and the nematodes Trichuris trichiuris from man, Tox- 

 ascaris limbata and Ankylostoma caninum from the dog, and 

 Sclerostomum equinum and Ascaris megalocephala from the horse. 

 Of these the following only are human parasites : T. trichiuris, 

 D. caninum, H. diminuta, and T. limbata. The main object of 

 Nicoll's experiments was to ascertain, first, to what extent, and 

 second, for how long a period flies could carry eggs by actually 

 ingesting them and retaining them within their intestines, and, 

 third, how gi'eat was the partiality they displayed towards feeding 

 on infective material. He points out that the only parasites with 

 which it is possible that flies can directly affect man are Taenia 

 echinococcus and T. solium together with the following species 

 which do not require an intermediate host : 



Class a. Those in which the larval worm remains within the 



egg-shell. 



Ascaris lumhricoiden, 

 Toxascaris limhata 

 Belascaris mystax 

 Oxyuris vermicularis 

 Trichuris trichiuris 

 Hymenolepis nana 



Class b. Those in which the larva is liberated from the egg- 

 shell and spends its life in water. 



Ankylostoma duodenale, size uf egg '060 mm. long, "040 mm. broad 

 Necator americanus „ „ '065 „ „ "040 



Schistosomum haematobium „ 

 Schistosomum japonicum „ 



