162 ] The Classification of Lower Organisms 



stage known Crithidia. 



2. Trypanosoma and crithidia stages un- 

 known Leptomonas. 



1. Attacking vertebrate animals. 



2. Trypanosoma stage known Trypanosoma. 



2. Trypanosoma stage unknown Leishmania. 



Man has been concerned particularly with Trypanosoma gambiense, the agent of 

 African sleeping sickness; T. Cruzi, the cause of Chagas' disease; T. Brucii, T. Evansi, 

 T. equinum, and T. equiperdum, which cause in domestic animals the diseases, 

 respectively, nagana, surra, mal de caderas, and dourine; Leishmania Donovani and L. 

 tropica, causing kala azar and oriental sore; and L. brasiliensis, causing espundia, 

 ferida brava, or chicleros' ulcer, usually appearing as a grievous disfigurement of 

 the features. 



Schaudinn (1903), having studied a trypanosome occurring in mosquitoes and in 

 the owl Athene noctua, described the nucleus as undergoing repeated unequal divi- 

 sions. It appeared to him that when a cell is to produce a flagellum, one of the 

 minor nuclei produced by unequal division generates it. Prowazek (1903) described 

 similar phenomena in a Herpetomonas occurring in flies. These reports led Woodcock 

 (1906) to apply to the proper nucleus of trj^panosomes the term trophonucleus, and 

 to the large granule near the base of the flagellum the term kinetonucleus. 



There has been much other study of the cytology of trypanosomes (as by Minchin, 

 1908, 1909; Robertson, 1909; Woodcock, 1910; Minchin and Woodcock, 1910, 1911; 

 Kiihn and Schuikmann, 1911; Minchin and Thomson, 1915; Schuurmans Stekhoven, 

 1919). This has not confirmed the foregoing accounts and conclusions, but appears 

 to have established the following points. 



The base of the flagellum is slightly swollen and may be construed as a blepharo- 

 plast. Separated from the blepharoplast by a distance of one or two microns there 

 is a conspicuous parabasal body (the kinetonucleus of Woodcock). Fine strands con- 

 necting the blepharoplast, parabasal body, and nucleus, have been observed. Most of 

 the stainable material in the resting nucleus is aggregated in a globular karyosome. 

 In mitosis, the karyosome breaks up to form a moderate number of chromosomes and 

 a central granule, evidently a centrosome, which stains more heavily than the chromo- 

 somes. It divides before the chromosomes, the daughter centrosomes remaining con- 

 nected by a fine fiber, the centrodesmose. An obscure spindle forms about the centro- 

 desmose; thi' chromosomes undergo division within the spindle, and the daughter 

 chromosome > assemble about the centrosomes. Mitosis is completed by constriction 

 of the nuclear membrane. 



The blepharoplast divides at the same time as the nucleus. The flagellum splits 

 to a short distance and one of the branches breaks loose; one daughter blepharoplast 

 retains essentially the whole of the original flagellum while the other generates one 

 which is almost entirely new. The parabasal body undergoes constriction. The cell 

 membrane cuts in in such fashion as to divide the cell longitudinally. The blepharo- 

 plast and the parabasal body persist through the non-flagellate leishmania stage. 

 Reports that the nucleus may generate these structures, or that one of them may 

 generate another, were apparently mistaken. 



Schaudinn described complicated processes by which a trypanosome generates 

 differentiated male and female gametes which duly undergo syngamy. His account is 

 believed to have resulted from mistaking stages of a sporozoan for those of a trypa- 

 nosome. Still, the occurrence of syngamy among trypanosomes is inherently probable. 



