(4) The glands have often suppurating points due 

 to streptococcus infection. 



Transmission* From an infected to a healthy 

 individual is effected by GL palpalis, and almost 

 certainly by other species, though these have not as yet 

 been accurately determined. The transmission is 

 direct, i.e., the fly passes straight from the sick to the 

 healthy person ; in fact, according to experimental 

 evidence on animals, the fly cannot infect a second 

 animal, as the adherent trypanosomes are cleared off in 

 the skin of the first animal bitten. Further, the fly that 

 has bitten an infected animal ceases to be infective on 

 the next day, and probably much earlier (? a few hours). 

 In spite of this fact, the trypanosomes are said to 

 undergo the following changes in the mid-gut of the fly, 

 (i) In twenty-four hours two kinds of trypanosomes 

 appear, (a) the female, with sluggish motion, large with 

 granular and deeply staining cytoplasm ; the nucleus 

 is large and spherical, the free flagellum is short, and the 

 blepharoplast is some way from the posterior end (Fig. 

 1 08). These are rare in blood films. () The male 

 actively motile and slender, cytoplasm non-granular, 

 nucleus usually compressed, free flagellum long. These 

 are common in blood films. (2) In forty-eight hours 

 trypanosomes of an indifferent type appear. These are 

 the type that prevail in blood, and have a short free 

 flagellum. (3) In ninety-six hours all trypanosomes have 

 disappeared, nor can they be found in any other of the 

 flies' tissues. If development now proceeds in some 

 unknown way, then the fly must become infective again 

 later. It does not appear that experiments have been 

 made with flies kept for long periods. 



A certain percentage, one to seven per cent., of tsetse 

 flies, moreover, that have never fed on human blood and 

 possibly not on blood at all, contain trypanosomes in 



* Also occurs through sexual intercourse in some cases (Koch). 



