350 FAMILY: TRYPANOSOMID^ 



extent on the amount of blood present. The flagellates have a marked 

 tendency to attach themselves to the lining epithelium, which may be 

 completely covered with a mosaic of flagellates, mostly of a stumpy type. 

 It is by the flagellar end that attachment is made, and the flagellum 

 becomes much reduced in length till it is represented only by the axoneme; 

 the anterior end of the organism then lies in contact with the epithelial 

 cell. The majority of flagellates are attached to the epithelium, and this 

 is probably a result of the behaviour of the gut when the flea feeds. 

 During this act, by means of transmitted light, the gut can be seen to be 

 in a state of violent peristalsis, the waves passing first in one direction 

 and then the other. The result is that the first droplet of liquid ejected 

 from the rectum by the flea contains pure unaltered blood, and if the flea 

 has been feeding on a rat infected, for instance, with Trypanosoma lewisi, 

 the living trypanosomes may be found in the first droplet passed. It is 

 clear that if all the leptomonas were free in the gut cavity, the majority 

 would be voided with the dejecta. Only those forms which are free or 

 have become detached escape in the ejected blood, and in this all the 

 various stages of the flagellate which occur in the gut can be found. 

 When there is little nourishment in the hind-gut, practically all the flagel- 

 lates are in the attached condition, but after a meal of blood, many active 

 flagellates can be seen in the gut contents, the long flagellate forms being 

 developed from the shorter non-flagellate attached ones. The infection 

 may spread into the Malpighian tubes, where the same series of free and 

 attached forms are to be found. Towards the posterior end of the intes- 

 tine the attached flagellates, and also those free in the cavity, become 

 smaller, till finally little ovoid leishmania forms are produced. These, 

 together with all the larger forms up to the longest flagellates, are found in 

 large numbers in the faeces of the flea, which consist of droplets of digested, 

 semi-digested, or pure blood. The flea has such a voracious appetite that 

 it will continue to feed for a long time, filling its stomach again and again 

 with fresh blood, while it repeatedly voids what is apparently pure blood 

 from its rectum. The general rule is that the largest flagellates are found 

 in the fore part of the hind-gut, either free or attached, and the smallest 

 forms in the rectum, but this rule is not absolutely constant. Sometimes 

 the whole gut is lined with short stumpy forms with very few long forms, 

 at others there is a larger number of long forms. In attachment there is a 

 tendency for groups of flagellates to be arranged as a disc, with the flagella 

 directed towards the centre or in a hemispherical mass, the so-called 

 rosette, which has its base on the epithelium, the flagella of the individual 

 flagellates being directed centrally. Such groups increase in number till 

 the whole gut is covered. In these groups all individuals may be long or 

 short forms, or a single group may show every transition from the largest 



