706 ), A. MINCHIN. 
due to variability in the objects themselves, I have made use 
in these researches of the common trypanosome of the rat, since 
it can be obtained in a practically monomorphic condition and 
does not exhibit the remarkable polymorphism shown, for 
example, by the trypanosome of sleeping sickness. Moreover, 
after about the tenth day of infection all multiplication ceases, 
and though individuals may be found occasionally with two 
or even three trophonuclei, | am convinced that this condition 
has nothing to do with division, as has sometimes been 
supposed, but is to be regarded as an abnormality. Hence in 
Trypanosoma lewisi, after the multiplication-period is over, 
the variability in size and structure is reduced to a minimum, 
and the details of cytological structure are not complicated by 
changes due to processes of fission or multiplication. 
This memoir is divided, therefore, into two parts. In the 
first part I shall deal with the subject from the point of view 
of the technique, and discuss the results obtained by different 
methods of fixing, staming, etc., under their respective 
headings. In the second part I shall discuss the structure of 
the trypanosome itself, taking its various parts in order. In 
dealing with two subjects which, though distinct, necessarily 
overlap to a certain extent, it is very difficult to avoid repeti- 
tion, and though I shall try to steer clear of this defect in 
exposition as much as possible, | must crave indulgence in 
those parts of my subject where repetition is an alternative 
to omission of necessary statements. 
Part I.—TEcHNIQUE. 
The subject of modern microscopical technique is an 
absolutely inexhaustible study ; no one in a human life-time 
could claim to have said the last word upon it. As I write, 
all sorts of methods that I have not tried, or variations 
upon methods that I have tried, present themselves to my 
mind. It becomes necessary in a research of this kind to 
set a term to one’s work, and to rest content at a certain 
period with what one has achieved, however incomplete it 
