152 HUMAN INTESTINAL PROTOZOA IN THE NEAR EAST 



In so doing the flies removed most of the faeces, the remainder 

 drying so that all the cysts were killed. The above-mentioned 

 observers (Kuenen and Swellengrebel) failed to demonstrate the 

 passage of cysts through the intestine and so concluded erroneously 

 that flies were of little consequence in the distribution of the cysts 

 of E. histolytica. The experiments we have made entirely disprove 

 this assumption, for with the rapid passage of ingested cysts through 

 the intestine the fly becomes a very potent factor in the spread of 

 amoebic dysentery. 



These experiments have been conducted with the ordinary 

 house-flies (Musca and Fannia), and with the blue-bottle fly 

 (Calliphora), and the green-bottle fly (Lucilia). We have observed 

 the passage through all of these of the cysts of E. coli, E. histo- 

 lytica and L. intestinalis. Quite recently we have examined 200 

 wild house-flies captured at random in different localities in 

 Alexandria. The flies were given no food whatever by us, but were 

 allowed to deposit their faeces in glass tubes. It was evident that 

 many of these had been feeding on human faeces, and in the 

 droppings of fifteen we found not only the cysts of E. histolytica, 

 f E. coli and L. intestinalis, but also the oocyst of a coccidium and 

 the eggs of various parasitic worms (Tcenia saginata, Ankylostoma 

 duodenale, Trichocephalus trichiurus, Heterophyes heterophyes, and 

 the comparatively enormous lateral-spined egg of Bilharzia). One 

 fly which deposited cysts of E. histolytica was actually captured 

 in a cook-house. It is evident, therefore, that flies under natural ") 

 conditions are actively concerned in the carriage of the cysts of C 

 the dysentery amoebae and other organisms. Of the 200 flies the / 

 droppings of which were examined, fifteen were found to have 

 deposited cysts of protozoa or eggs of parasitic worms. All the 

 infected flies came from near the cook-house of a hospital compound 

 which was separated from a native village by a single wall. 



(B) EXPERIMENTS ON THE RESISTANCE OF CYSTS. 



The great difficulty in studying the resistance of the cysts is 

 the want of a reliable test as to their viability. Kuenen and 

 Swellengrebel employed the eosin test, which seems to us fairly 

 trustworthy. It is generally agreed that a living cell will not stain 

 with dilute eosin, whereas a dead cell will stain at once. This test 

 can be readily illustrated by the action of heat on the cyst of 

 E. coli, E. histolytica and L. intestinalis. Faeces containing 



