510 
ZOOLOGY: R. ERDMANN 
and divisions were noticed. The following day small actively motile 
forms appear (fig. 3, c and d). These are all without discernible nucleus 
when observed by dark-field illumination. In subsequent days these 
forms become smaller and do not change for an unlimited period, pro- 
vided the organisms are transferred into new plasma under sterile con- 
ditions. Often they seem motionless, then again they have a cork- 
screw-like motion in the plasma. Frequently they flatten out, like a 
disk, or their edges fold over. 
The preparations of preserved specimens show divisions into four and 
eight individuals as well as single individuals and, very rarely, the round 
forms, such as have been already described from the higher temperature 
(figure 2, b, c, d, e, f, g and h). Besides these forms similar to those 
described in plasma at 37°C., other types were found at 16° to 18°C. 
(fig. 4, a, b and c). Pear-shaped individuals are observed lying in clus- 
ters of from four to eight. The relative position of nucleus and ble- 
pharoplast has become changed in some of the animals observed at this 
period. The basal granule could not be distinguished, but the fiagellum 
seems to arise from the blepharoplast. Figure 4, a shows such an animal, 
which perhaps might be termed crithidia-like because of the nucleus and 
the blepharoplast and the absence of an undulating membrane. This is 
the most frequent form in the plasma, and may be found even 30 days 
after the plasma is inoculated. These forms divide but undergo no fur- 
ther morphological changes. 
Rounded forms of the above mentioned type (fig. 2, g and h), and of a 
slightly difterent type can also be observed on the fifth, sixth and seventh 
day after inoculation into the plasma (fig. 4, c). In these the fiagel- 
lum has disappeared and only a tail of protoplasm is to be seen. 
They have a slight resemblance to the Dauerstadien in the frog try- 
panosome described by Dofiein^^ except that in the latter forms the 
protoplasmic ^tail' has disappeared. In brief then, the full grown 
trypanosomes, in the plasma, at a temperature of 16° to 18°C., undergo 
changes which frequently lead to the formation of crithidia-like forms, 
and also sometimes, but rarely, to rounded forms. 
After discovering that the crithidia-like and the rounded forms do 
not undergo further changes in the plasma (they were in the plasma 
from February 13 to 21), I inoculated them again into the rat. Five 
days after this inoculation small forms were observed (fig. 5, a, b). 
These were full grown at the seventh day (fig. 5, c) and caused the death 
of the rat at the ninth day of infection. Figure 6, which presents ani- 
mals from another but exactly similar experiment, gives a good idea 
of these forms, which are present in the rat's blood on the fifth, sixth and 
