10 
p 
saw them disappear from the blood in some cases in from one to two ? 
weeks, sometimes earlier. Two rats retained their parasites three to j 
four months. j 
Wasielewski and Senn found trypanosomes five and one-half months j 
after injection in several instances and no animal lost his parasites ' 
before six weeks. 
Jnrgens (6) found that his animals kept their blood parasites as a 
rule one to two months, seldom later. In two cases numerous para- 
sites were found after seven months. Only once did he find the 
infection to last shorter than one month. j 
We found the duration of the infection to be seven to fourteen days, j 
The long periods of infection of three to six months, or even of six ! 
weeks, we have not seen. The trypanosomes never returned spon- ; 
taneously to the rats after they had once become free of them. We | 
were unable to find any wild rats infected spontaneously, but the ] 
duration of such an infection is, according to Rabinowitsch and I 
Kempner, much longer than an artificial infection of white rats. i 
They state that in an infection of the wild rats the parasite, so far as | 
they have observed, did not disappear from the blood. j 
MOTION OF THE TRYPANOSOME. j 
If a thin film of fresh blood is watched beneath a cover slip on a 
slide the parasites are seen to be in striking activity, darting among 
the corjDuscles and pushing them aside, but never entering the cor- 
puscles or engulfing them. The motion is too violent to be closely 
followed by the eye, so in order to gain an accurate perception of the ' 
mechanism of the motion the film must be very thin, so that the ' 
trypanosome will be subjected to the pressure between the cover and 
slide, and consequentl 3 ^ his motion becomes very slow. | 
We see that the parasite generall}^ moves with the fiagellum (anterior 1 
end) in front, but if he meets an obstruction he withdraws for onl^^ a 
short distance in the direction of his blunt (posterior) end, and then ■ 
resumes in his original direction. The movement takes place by ■ 
means of the undulating membrane and the flagellum. When in I 
motion the body of the parasite rotates on its longitudinal axis, thus j 
moving in a screw-like manner. This causes the undulating mem- ! 
brane to appear as if it were spirally arranged around the organism, i 
The waves, starting in the flagellum and traveling along the undulat- , 
ing membrane, are plainl}^ seen. Motion will persist in a cover glass i 
preparation for several hours. ,, 
SYMPTOMS IN RATS. 
Rabinowitsch and Kempner mention loss of appetite, slight loss of » 
weight and debility, but sa}^ that none died from the infection. They i 
regard the disease in white rats as mild compared with the same in ‘ 
wild rats. . \ 
Jurgens reports severe sickness and death. : 
