ZOOLOGY: R. ERDMANN 
511 
seventh days after the crithidia-like forms are reinoculated into the rat. 
The individuals shown in figure 6, f and g, are probably identical with 
the forms illustrated in figure 5, a and b. It is evident from these 
figures that animals with typical trypanosome form are not present in 
the blood at this period. However, that the forms which are present 
develop in the blood into Trypanosoma brucei has been proved by four 
experiments in which the inoculation of crithidia-Hke forms was carried 
out (fig. 5 c). The typical trypanosome forms did not always appear 
after the first inoculation of infected plasma into the rat. Sometimes 
two or three passages were necessary to effect this phenomenon — but 
sooner or later Trypanosoma brucei with its characteristic form was 
present. Every precaution was taken to exclude possible sources of 
error by contamination, etc. The blood of all rats employed was 
examined before inoculation for Trypanosoma brucei. The animals 
were kept in a room where animals with Trypanosoma brucei had never 
been before, and further, the rats were etherized to eHminate the highly 
improbable source of infection, the rat flea. This new strain M proved 
highly virulent and caused the death of the rat in three days. 
An attempt was made to determine in what organ of the rat the 
crithidia-like forms and the rounded forms underwent transformation 
into the typical trypanosome form. Pieces of spleen, liver, heart and 
lungs of rats, infected with these forms, were implanted into plasma and 
kept alive and growing for a considerable time. Study of these tissue 
cultures failed to reveal any full grown trypanosomes. Only twice 
were even crithidia-like forms found in a culture of lung tissue. It is 
necessary for these experiments to be repeated on a larger scale for it 
is certain that rats infected with crithidia-like forms carry them, or 
young trypanosomes, for a considerable time. It is quite probable 
that this phenomenon goes on in nature and that some wild animals 
are the carriers of the infection by means of the form under discussion, 
even where full grown trypanosomes cannot be detected. 
Finally, I shall briefly describe some changes in Trypanosoma brucei 
in plasma which I have succeeded in obtaining but once. The experi- 
ment was started in the same way and under the same conditions as 
outlined above, the plasma being kept at 16° to 18°C., etc. After twenty- 
four hours numerous trypanosomes without definite nucleus appeared 
(figure 7, b, c, d, e). They resemble the forms of Trypanosoma brucei 
which Bradford and Plimmer^^ observed in the lungs. These animals I 
found dividing rapidly until at the third day two types were present as 
shown in figure 7, f and g. The following day also two different types 
could be distinguished: animals with a clearly defined nucleus, but with 
