23 
parasite was perhaps excluded by our filtration experiments. Try- 
panosome blood was diluted with fifteen parts of physiological salt 
solution and subjected to a porcelain filter under the influence of a 
vacuum. The filtrate was found to be noninfective to rats. 
In blood kept in the ice chest for eighty-one days we found living 
trypanosomes. Their motion was of a trembling, vibrating character. 
Very few crossed the field. Many were arranged in rosettes. In the 
stained preparations we found parasites in which the positions of the 
centrosome and nucleus were reversed, the centrosome being anterior 
to the nucleus. In many of the trypanosomes there was granular 
degeneration, and there was also much free granular debris, which 
probably represented the remains of degenerated parasites. At room 
temperature and at 37° C. the parasites are short-lived. The different 
investigators found them capable of producing an infection of rats 
after being kept in the incubator and at room temperature from four 
to seven days. The parasites when kept at 12° to 16° C. in sterile 
pipettes can maintain their vitality very much longer than under any 
other condition. 
Laveran and Mesnil kept parasites alive in defibrinated blood or in 
equal parts of defibrinated blood and physiological salt solution for 
forty-seven days in the ice box. At the end of this time the blood 
was injected into rats and produced a blood infection in nine days. 
In blood kept under the same conditions for fift3^-one days they saw 
no parasites by microscopic examination, but it was infective for rats. 
Jurgens found only a few parasites in blood kept in the ice chest 
for fifty- three days, but rats injected with it showed parasites in their 
tail blood after seven days. 
Bacteria have a very detrimental effect on the life of the parasites 
outside the body. In hanging drops of trypanosome blood which 
has become infected with bacteria the parasites rapidly die. Blood 
drawn for keeping in the ice box must be kept under sterile condi- 
tions. Trypanosomes are killed after an exposure of a few minutes 
at 55° C. Wasielewski and Senn found living trypanosomes in the 
bloody urine of a rat. Rabinowitsch and Kempner were never able 
to find the parasites in the feces or urine. 
THE TRYPANOSOME OF THE HAMSTER. 
This animal harbors a parasite which has been studied by Rabino- 
witsch and Kempner. They find that it resembles the rat trypano- 
some in that it can hardly be differentiated from it morphologically 
and has the same process of development. On the other hand, they 
could not convey it to rats, and some of the rats Avhich were refractory 
to hamster trypanosomes later proved susceptible to rat trypanosomes. 
These facts, taken together with the fact that they could not convey 
rat trypanosomes to the hamster, led them to conclude that the ham- 
ster trypanosome and the rat parasite represent two different physio- 
logical varieties, which morphologically are almost inseparable. 
