149 



"THE CARRIAGE OF CYSTS OF ENTAMCEBA HISTO- 

 LYTICA AND OTHER INTESTINAL PROTOZOA AND 

 EGGS OF PARASITIC WORMS BY HOUSE-FLIES, 

 WITH SOME NOTES ON THE RESISTANCE OF 

 CYSTS TO DISINFECTANTS AND OTHER AGENTS. 1 



THE importance of house-flies in the spread of various bacillary 

 infections of the intestine has been well established and though a 

 similar distribution of the infective agent in amoebic dysentery has 

 been suspected no very definite experiments have been made to 

 prove it. For this reason we feel that the observations to be 

 recorded below are of considerable importance, for they establish 

 beyond dispute the great danger of the house-fly as a factor in the 

 spread of the disease. 



Amoebic dysentery is caused by an amoeba, Entamoeba histolytica, 

 which lives in the large intestine, where it invades the wall of the 

 bowel and produces the dysenteric ulceration. 



'in the acute dysenteric process only the free motile amoebae are 



to be found in the faeces, but as the acute symptoms abate 

 smaller amoebae (minuta forms) occur and many of these become 

 encysted in the large intestine in transparent capsules, in which 

 condition they are passed from the intestine in the faeces in very 

 large numbers. The cysts of E. histolytica measure from six to 

 eighteen microns in diameter. On account of the capsule, they are 

 relatively hardy structures which, though they cannot withstand 

 drying, will nevertheless survive for considerable periods if they 

 remain moist. The spread of amoebic dysentery is determined by 

 these cysts, for if ingested in water or food each one gives rise to' 

 four amoebae under the influence of the pancreatic fluid. The four 

 small amoebae grow into adult forms of E. histolytica, which invade 

 the tissues of the large intestine and produce amoebic dysentery. 



The cysts are often passed in very large numbers by " carriers," 

 which are cases which have partially or apparently wholly recovered 



1 Memorandum published in Egypt, April, 1916. 



* Reprinted from the Journal of the Royal Army Medical Corps, May, 1917. 



