CHAGAS' DISEASE — PARASITE IN BUG 



111 



transmitting agent of the trypanosome. A few hours after a 

 bug has fed on infected blood the trypanosomes begin to change 

 form in the midgut, becoming round and Leishmania-like in form, 

 losing the flagellum and undulating membrane (Fig. 28A, B and 

 C.) Then comes a period of very rapid increase in number, the 

 parasites gradually pushing backward toward the hindgut by 

 sheer multiplication. After about two days Crithidia forms 

 begin to develop and become numerous in the hindgut, being 



Fig. 28. Development of Trypanosoma cruzi in digestive tract of bug (Tria- 

 toTna megista). A, freshly ingested form; B, rounding up and loss of flagellum, 6 

 to 10 hrs. after ingestion; C, LeishmaniaAike form in midgut, 10 to 20 hrs. after 

 ingestion; D, redevelopment of flagellum and undulating membrane, 21 hrs. after 

 ingestion; E and F, crithidial forms in hindgut, 25 hrs. after ingestion; G, trypa- 

 nosome form from salivary gland, 8 days or more after ingestion. (After Chagas.) 



voided with the excrement from time to time (Fig. 28D, E and F) . 

 It has been suggested that these crithidial forms do not play any 

 part in the transmission of the disease to man but that they rep- 

 resent a return to a primitive condition suited to existence in the 

 bugs, and that they may be transmitted from bug to bug in this 

 form, since the bugs are known to prey to some extent upon each 

 other and a^so upon their excrement. Torres, however, considers 

 transmission of the flagellates from bug to bug as very doubtful. 

 Chagas believes that there is a second cycle of development in 



