SPIROCHZTA BALBIANII AND SPIROCHMTA ANODONTA. 11 
which moves more rapidly, and so is difficult to keep in the 
field. 
In the case of each of the Spirochetes mentioned, the 
thickened border of the membrane could be observed in life, 
with comparative ease in 8. balbianii, with greater difficulty 
in S.anodonte. The spiral movements, and the undula- 
tions travelling down the body of the parasites while in active 
motion under the practically normal conditions, were thus 
observed. But these movements will be described in detail 
in the next section. 
I have also postponed all consideration and discussion of 
environmental effects and attempts at cultures of these para- 
sites until after my description of the normal forms, as seen 
in both living and fixed preparations. 
(6) For Fixed and Stained Material. 
Many methods of fixation and subsequent staining were 
tried, and the resulting appearances of the parasite were 
always carefully compared with those seen in life under 
normal conditions as far as possible. This procedure was 
adopted in order to eliminate, if possible, deceptive appear- 
ances or artifacts due to pathological changes or post-mortem 
effects. Where such abnormalities occurred allowances were 
made for them, as judged by observations on the actively 
living parasitic organisms. In this way an interpretation 
can be given of so-called flagellate or ciliate stages in Spiro- 
cheetes (see p. 32). 
Fixation.—Thin smears or films were made from the 
gut contents of the Lamellibranch hosts. The contents were 
taken up with a pipette and placed quickly on a slide, or a 
part of the infected crystalline style was quickly teased with 
needles while kept moist in alittle of its natural surrounding 
medium. Such preparations of gut contents, usually on 
slides or at other times on cover slips, were fixed, as 
quickly as possible, and while still wet, with osmic 
vapour. The spreading or thinning out of the film was 
