MASTIGOPHORA 1077 



and the kinetonucleus behind it, often at the posterior extremity. The 

 flagellum arises from a centriole (blepharoplast), which is located 

 close to or in the kinetonucleus, and quickly reaches the surface of the 

 body, when it turns forward and forms the border of the undulating 

 membrane, a thin fold of periblast running the entire length of the 

 body, and is often continued further forward as delicate filament. 

 During life the undulating membrane has a constant wave-like motion. 



Transmission from one animal to another is usually by means of 

 some blood-sucking invertebrate. Two possible forms of transmission 

 have been recognized, the direct and indirect or cyclical; the direct 

 form is used in the laboratory when transferring blood with a hypo- 

 dermic syringe from an infected animal to a healthy one, and it also 

 occurs in nature, although not so frequently as the second. Dourine, 

 or mal de coit, is the best example of the natural direct method. The 

 cyclical method is exemplified in the transmission of Trypanosoma 

 leAvisi by the rat flea, Ceratophyllus fasciatus, in which insect the 

 trypanosome passes through a complicated life cycle. Whether the 

 parasite in the insect ever passes from parent to offspring is still 

 doubtful. Among fishes, reptiles and amphibians the parasites are 

 carried by leeches, in whose intestinal tract they undergo a cycle of 

 development. 



Just as in malaria, there is usually an alternation of hosts, from 

 invertebrate to vertebrate, a part of the life cycle being passed in each. 

 In the blood of the vertebrate is found the fully developed trypano- 

 some, and in the intestinal tract of the invertebrate, crithidial. and 

 trypanomonad types, which are characterized by having the kineto- 

 nucleus placed in front of or close beside the trophonucleus and by 

 having a rudimentary undulating membrane. 



Cultivation. In 1903 Novy and MacNeal 2 first obtained pure cul- 

 tures of trypanosomes on artificial media. The medium devised by 

 them is prepared by equal parts of nutrient agar and defibrinated rab- 

 bit blood. After the agar has been melted and cooled to about 50 

 C. an equal quantity of rabbit blood is added, mixed and allowed 

 to cool. "The tubes thus prepared are allowed to set in an inclined 

 position, after which they are at once inoculated. It is essential 

 that the surface of the medium be moist and soft, and if this is 

 not the case, the tubes should be placed in an upright position until 

 some water of condensation accumulates at the bottom. The initial 



2 Novy and MacNeal, Contrib. Med. Eesearch (Vaughan), Ann Arbor, 1903, 

 p. 549. 



