BUGS AND KALA-AZAR 197 



once and to grow flagella (Fig. 39, B-E), just as the 

 pre-flagellate form of a Herpetomonas does. The 

 development went on best in the mid-gut of the bug, 

 and the flagellates (Fig. 39, K) formed there were 

 active and healthy. Multiplication by repeated longi- 

 tudinal division also proceeded (Fig. 39, F-H ) . Some 

 forms also divided before the flagella were produced, 

 but these developed flagella exactly as did those that 

 produced them previous to division. Finally, in the 

 far mid-gut and hind-gut the parasites gradually 

 reassumed the more resistant post-flagellate forms. 



The post-flagellates seemed to be the form most 

 suited for direct transmission to man. When bugs 

 begin to suck blood, a small quantity of their gut con- 

 tents is regurgitated. There is no mechanism in the 

 insects' gut to prevent this. With the fluid thus 

 expelled are probably some of the post-flagellate 

 parasites, and these, entering the wound, may be 

 seized upon by the leucocytes which, however, are 

 incapable of destroying them. There they may grow 

 and multiply, and finally, having destroyed their host 

 cells, they may be set free into the blood-stream. 

 Such is a possible sequence of events, should Kala- 

 azar be transmitted by the bed-bug. 



Now, the organisms do not possess flagella while 

 in the human system, and consequently cannot swim 

 about in the blood-current as trypanosomes do. As 

 a result, they are found in greatest numbers in 

 those organs that may be described as backwaters of 

 the blood-stream namely, the spleen, which becomes 

 enormously enlarged, the lymphatic glands, the bone- 

 marrow, and the liver. The number present in the 



