NEW TYPE OF PKOTISTAN PARASITE. 
437 
just referred to, though they were frequently examined 
during two days, we never found any active parasites after 
about four hours. The third goat examined furnished a 
remarkable illustration of this point. It was killed, and 
quantities of the rumen contents, taken from different parts, 
were put into two small dishes, which had been previously 
warmed. Not more than a quarter of an hour elapsed 
before these were examined, but although the crescents were 
extremely abundant, not one of them was active, though the 
flagellum could be made out in many. A warmed pipette 
was then taken and a fresh quantity of the contents obtained 
and immediately looked at; in the cover-slip preparations made 
here and there were areas of active parasites, though in other 
places they were motionless. 
We consider that, in general, it is the lowering of the 
temperature which renders the parasites motionless, though 
we have come across exceptions. Thus, on one occasion, in a 
cover-slip preparation which had been kept at about 30° C. for 
twenty-four hours, a few parasites were still feebly motile. 
Again, in an endeavour to cultivate the parasites on agar 
plates, we have found two or three individuals still motile 
five days after being removed from the goat. In this character 
of extreme susceptibility to change of environment, Seleno- 
mastix agrees with the peculiar Ciliates and the Flagellates 
also present in the rumen ; the Heterotrichous forms (Ento- 
dinium, Oph ry oscol ex) are even more quickly rendered 
motionless — indeed, frequently one can no longer find an 
individual still active — while the Flagellates are apparently 
just about as susceptible as Selenomastix, remaining active 
for two or three hours. On the other hand, the motile bacteria 
which occur (bacilli, spirillar forms) remain active for a much 
longer time. 
We may add here that no development of the parasites 
occurs when cultivated outside the body, so far as we have 
been able to ascertain. We have tried simple agar plates, 
varying the strength and consistency of the medium. There 
is no further multiplication or apparent increase in number 
