786 E. A. MINCHIN. 
Beautiful preparations of collar-cells can be obtained by 
fixation in osmic acid followed at once by staining with 
picrocarmine; the same method is absolutely useless for 
trypanosomes. ‘lhe osmic-picrocarmine method shows the 
uucleus of the collar-cells as a deeply stained pink mass, in 
which a nucleolus can just be made out, but beautiful pre- 
parations of nuclear structure in collar-cells can be obtained 
by fixation in Flemming’s or Hermann’s fluids followed by 
Delafield’s hematoxylin, safranin, gentian violet, methylene- 
blue-eosin, etc.—just the methods, in fact, which I used on 
trypanosomes with such ill success (but with excellent results 
on the leucocytes). 
It seems to me, therefore, quite illogical to argue that a 
method is good or bad for trypanosomes or any other cells, 
because it is good or bad for some quite distinct class of 
object. Every kind of cell requires its own special technique, 
which must be established empirically by trial, and can be 
discovered only to very limited extent and with great 
uncertainty by analogy. 
Part IJ.—Tse Srrucrure or ‘'rypanosoma Lewis!. 
(1) General Structure, Form and Dimensions. 
As I have stated above, I believe that the preparations 
fixed simply with osmic acid vapour, and examined in the 
blood with or without addition of acidulated methyl-green 
but without further treatment of any kind, represent the 
nearest possible approach to the living condition in form and 
dimensions. In such “ standard ” preparations (figs. 1-8) the 
body of the trypanosome appears long and slender, sharply 
marked off from the distinct undulating membrane and 
flagellum. ‘The kinetonucleus is seen near one extremity, 
which for convenience may be termed “ posterior.” ‘lhe 
trophonucleus is seen as an oval, well-defined space, containing 
the distinct karyosome, and situated at rather more than two 
thirds the length of the body from the posterior end. We 
