594 FAMILY: TRYPANOSOMIDiE 



into the proboscis sheath, where they multiply rapidly. Infection takes 

 place from the proboscis sheath during the sucking act. After feeding, the 

 leech has emptied its proboscis sheath and multiplication of the trypano- 

 somes commences again in the stomach, and reinfection of the proboscis 

 sheath again occurs towards the end of digestion. The development in the 

 leech takes place in the stomach alone, the intestine being free from 

 flagellates. 



No intracellular stage was observed in the leech, nor did the trypano- 

 somes invade the body cavity. As Noller points out, it is remarkable how 

 easily the young leeches infect themselves from tadpoles which have a very 

 scanty infection of trypanosomes. Over a hundred young leeches were 

 thus infected. On the other hand, twenty-six leeches had a full feed on an 

 adult frog, in the blood of which occurred the large solid giant forms as 

 well as the thin leaf-like ones. Not a single leech was infected, though 

 they were kept under the same conditions as regards temperature as the 

 others (10° to 20° C). It might be urged that the trypanosomes of the 

 adult frogs belonged to a different species from that of tadpoles, but this 

 view is not tenable, as occasionally the young frogs show the typical 

 tadpole forms, while the frogs raised from the tadpoles only showed the 

 larger forms. For these and various other reasons, Noller concludes that 

 the typical tadpole forms become transformed into those which appear in 

 the frogs on account of change in the character of the blood associated 

 with the metamorphosis of the tadpole into the frog. 



Culture. — T. rotatorium is readily cultivated in blood-agar medium. 

 Of special interest is the behaviour of the large trypanosomes in vitro. 

 The phenomenon was first observed by Danilewsky (1885a, 1889) and 

 Chalachnikov (1888), and was later observed by Mathis (1906), Franga 

 and Athias (1907), Button, Todd, and Tobey (1907), LebedefE (1910), 

 Doflein (1910), and lastly by Ndller (19136). It consists of the rounding- 

 ofE of the trypanosome and its segmentation into a number of small 

 individuals. The accounts differ somewhat in details, the following 

 being based on the work of the last-named author. A drop of blood 

 from a frog was diluted with a similar quantity of bouillon, and a moist 

 preparation made and sealed to prevent drying, and examined at ordinary 

 laboratory temperature (10° to 25° C). If one of the large solid striated 

 trypanosomes (type 2) is kept under observation, it will be found to lose 

 its membrane and flagellum. Furthermore, the longitudinal markings 

 disappear, and, owing to various fibrous structures which appear adherent 

 to the cytoplasmic mass, it seems as if the striated periplast is thrown off. 

 Nuclear division can be seen to take place, and finally after about five to 

 six hours the cytoplasm divides, the two daughter individuals remaining 

 side by side. Each daughter then divides again, and the process is 



