10 H. B. FANTHAM. 
At other times hanging drops of the parasites in their 
natural medium were made and examined. Such prepara- 
tions, securely vaselined round the edges, were carefully 
observed under the microscope. Similar preparations of the 
gut contents were placed under a cover-glass supported on 
the slide by wax feet at the corners, and then vaselined 
round the edges. 
Methylene blue was tried as an intra vitam stain and 
was found successful. The Spirochetes, while still alive, 
stained deeply with a half-per-cent. solution of this dye in 
sea water or fresh water as the case might be, but usually 
died in about half-an-hour. Near the edges of the prepara- 
tion, or in a part where the methylene blue solution (after 
being run under the cover-slip or added to water containing 
the parasites) seemed less concentrated, there the Spirochetes 
remained alive some time longer; but they were not very 
active under these conditions. 
Examinations were made, from time to time, of the media 
in the aquaria or basins in which the Lamellibranch hosts 
were kept during these investigations. In this connection it 
is interesting to be able to record that Spirocheta bal- 
bianii was found moving about freely in two different basins 
of sea water in which specimens of infected English oysters 
were kept, the shells of these being still partly covered by 
mud from their native beds. I was able to demonstrate this, 
with living specimens, to some of my friends. 
These various preparations were observed under Zeiss 
AA, Zeiss DD and one-twelfth inch oil-immersion objectives, 
with Huygenian eye-piece 4. In the case of 8S. balbianii 
the one-sixth inch (Zeiss DD) was found most useful, for the 
parasites move very rapidly and over a large field. It is 
rather difficult to keep the organism under the comparatively 
limited field of an oil-immersion lens and, of course, the 
working distance is small. 
However, such an examination was conducted, but it added 
little to the observations made with a Zeiss DD lens. A simi- 
lar procedure was followed in the case of 8. anodonte, 
