304 Report on an Inquiry into the Nature, Causes, and 
that I should mention the following observation, made in their 
course. That flagellated protozoa may exist in the blood of 
healthy animals is now well known from the observations of 
Rattig, Wedl, Lewis, and others. But I am not aware of any 
similar recorded observation, and it may be found to have a 
pathological bearing at some future date. 
An apparently healthy white mouse was inoculated in the 
tail with some blood from the diseased quarter, and as it pre- 
sented no symptom beyond some swelling of the tail, it was 
supposed to have escaped all mischief. However, the swelling 
did not subside, but became gangrenous, and towards the middle 
of the second week it began to emaciate and the belly swelled ; 
finally, it died on the fourteenth day after the inoculation. 
Examiimtion Jive hours after Death. — On opening the abdomen 
there was found to be considerable opalescent exudation in the 
peritoneum ; the abdominal wall was also swollen and infiltrated. 
The tail, where inoculated, was considerably swollen. The 
other organs were fairly healthy. Before, however, I examined 
the organs, I took, as usual, some of the exudation in capillary 
tubes, and also some serum from the pleura and pericardium, 
and examined these microscopically. 
I naturally anticipated that I should have found the ordinary 
characters of semi-purulent serous effusion in the peritoneal 
iluid, but my astonishment was great when I found the fluid to 
be swarming with minute organisms swimming actively about 
in every direction, moving apparently by means of two long 
cilia or flagella. 
These organisms I may now describe more fully. They were 
ovoid, rounded, or more commonly, when in motion, pyriform 
or balloon-shaped ; very translucent, of delicate hyaline struc- 
ture, sharply defined. At the posterior extremity were two long 
fine lashes, moving with a wavy motion, much like that of cilia, 
and apparently serving to propel the organism forwards. In 
each could be seen a central clear space running lengthwise, 
wider at its central part, and apparently contracting and expand- 
ing. At the anterior extremity a more refractile part could be 
seen, apparently forming a sort of oral aperture. Their proto- 
plasm was highly contractile, and they changed shape, elon- 
gating and contracting very readily. In size they were, when 
at rest and round, about from 2 to 4*5 fj, in diameter ; when 
elongated, some reached 6 in length, and 1 '5 to 2 in width. 
I was able to observe their movements for more than half an 
hour, but it was not until they were quiescent that the other 
cilia could be seen, and they were not well seen until stained. 
A more thorough study of their character was possible after 
staining with methylaniline violet, and mounting in glycerine 
