THE STRUCTURE OF TRYPANOSOMA LEWISI. 763 
downwards, is placed on the glass ring, to which it sticks by 
means of the wet blood itself, and makes a practically air- 
tight chamber. A certain amount of the smear has to be sacri- 
ficed, of course, by this method, but there is always enough 
for all practical purposes preserved within the ring. After 
sufficient exposure the coverslip is lifted carefully off the ring 
and dropped at once into absolute alcohol or other fixative. In 
this method the only precaution necessary is the protection of 
the operator’s eyes and air-passages from the vapour of the 
osmic acid, It is advisable either to wear protective 
spectacles or to have the osmic cell covered with a glass 
plate, which an assistant removes the instant it is desired to 
place a coverslip on it. 
Salvin-Moore and Breinl (1907) recommend making smears 
on slides previously covered witha thin layer of glycerine and 
albumen, but with what object I do not understand, as the 
blood-films always stick on perfectly well to the coverslips and 
slides when plunged suddenly into fixatives, and neither cor- 
puscles nor trypanosomes come off. Even when working with 
fish-blood, in which the parasites are exceedingly scanty, I 
have always found them in my never-dried smears just as 
abundantly as in those done by other methods. In our 
technique the frail bodies of these unfortunate creatures are 
subjected to so many processes of violent treatment that to 
avoid deformation it is better to reduce and eliminate these 
processes as much as possible rather than to increase 
them. The addition of glycerine and albumen to the fresh 
blood containing living trypanosomes can but be an addi- 
tional source of error, and is therefore, in my opinion, best 
avoided. 
I made several attempts to obtain preparations of trypano- 
somes by the method recommended by Schaudinn (1902, p. 
190) for malarial parasites, that is to say by dropping fresh- 
drawn blood into fixatives, such as. Flemming’s fluid or 
Schaudinn’s fluid, in a centrifuge tube, and then carrying out 
all the subsequent processes of washing, staining, etc., by 
means of the centrifuge. After much searching I found some 
