TRYPANOSOMES 18 



in invertebrate hosts or in artificial cultures. It 

 is also of great interest that they are found in the 

 milky juice of certain plants (EupJiorbiaceae). 

 . 5. Leishmania. — There is no flagellum, but there are 

 two nuclei as in the other genera. These animals 

 have become specialized to live in the tissue cells 

 of vertebrates and so have no need of organs of 

 locomotion. It is of much interest that in arti- 

 ficial cultures Leishmania develops into forms like 

 the two preceding genera or like Trypanosomes. 

 The type species causes a fatal disease in Asia 

 known as " Kala-azar." 



Now let us consider a little more fully the Trypanosomes 

 themselves. They are elongated bodies with a pointed 

 posterior extremity where is a small nucleus, and at the 

 anterior extremity the whip-like flagellum which by vigor- 

 ous movements drags the Trypanosome along. The 

 undulating membrane pursues a wavy course along the 

 body and is responsible for the name, which is derived 

 from rpvTTavov, meaning a carpenter's tool : the allusion 

 is probably to the spiral thread on an auger. In the 

 middle of the body is a large nucleus. T. gambiense 

 in the blood is several times as long as the diameter of a 

 red corpuscle, but much narrower. The different species 

 that may be found in the blood vary very greatly in size 

 and activity ; gambiense is not very active and merely 

 wriggles, but a species such as vivax in goats can hardly 

 be kept in the field of a microscope. The first one to 

 be seen was found in the blood of a frog, but the 

 first reliable description was not given until 1841, when 

 a specimen was described from the blood of a trout. ^ 

 Not until 1879 was one found in a mammal, and this was 

 Trypanosoma lewisi, seen in the blood of the rat. It is 



1 By Valentin. Recent work by Mile. M. Gauthier, however, placoa 

 this species in the genus Trypanoplasma. 



