THE GENUS TRYPANOSOMA 253 



when mammalian blood and organisms are taken into the digestive 

 tracts of different insects (T. brucei disappears from the tsetse in from 

 two to three days). 



It is quite otherwise with cultivation on artificial media first suc- 

 cessfully accomplished by Novy and MacNeal, in 1903, with T. 

 lewisi. These keen investigators opened a new era by this application 

 of bacteriological culture methods with pathogenic protozoa, the 

 method, as we have seen (p. 239), giving excellent results with seem- 

 ingly obligatory cytozoic forms (Leishman-Donovan bodies). The 

 culture medium is made up of nutrient agar and defibrinated rabbit's 

 blood. \Mien desired for use the agar is melted and cooled to about 

 50° C, the blood added and thoroughly mixed. The organisms collect 

 and multiply in the water of condensation or even on the agar directly. 

 It was found that the organisms gradually lose their virulence and die 

 as a result of the exhaustion of the food medium, but that renewed 

 virulence and vitality could be established by transplanting to fresh 

 culture tubes. In this way Novy and his associates have maintained 

 trypanosomes in pure culture for several years. While T. lewisi 

 appears to be an especially favorable subject for this method of re- 

 search, other forms as well have been studied in this way, Novy and 

 MacNeal being successful with T. brucei, T. evansi, and with several 

 bird trypanosomes, while Laveran and Mesnil have succeeded with 

 T. brucei, dimorphon, T. gainbiense, and others. 



A. The Motile Apparatus of Trypanosomes. — In fresh blood 

 the presence of trypanosomes, when abundant, may be easily noted by 

 the agitation of the blood corpuscles, which are whipped about by the 

 lashings of the ever-active flagellum. This movement of the trypano- 

 somes may be analyzed as a combination of snake-like undulations, 

 active bending, rotation, and translation. In some, notably in T. 

 vivax, the peculiar writhing movements without progression, which 

 are characteristic of a great many species, are replaced by an active, 

 business-like forward movement in straight lines across the field of the 

 microscope. In such movement the flagellum, as with free-living 

 flagellates, is always in advance. 



As shown in Chapter I, the flagellum of a typical mastigo- 

 phoran is formed by the outgrowth of substance from the kinetic 

 centre, which may be in the form of a basal granule or blepharoplast, 

 or in the kinetic material within the nucleus. Such kinetic centres 

 have the appearance and often the functions of centrosomes, so that 

 the term centrosome sometimes used for the basal granule has some 

 significance. 



In trypanosomes, the flagellum has the same mode of origin as in 

 other flagellates, coming from a basal granule or blepharoplast which 

 may or may not be included in the kinetonucleus. In some cases, 

 during division of the cell, it appears to divide longitudinally as it does 



