THE STRUCTURE OF TRYPANOSOMA LEWISI. Mee 
may appear to oneself or to others. Circumstances, into 
which I need not enter, oblige me to break off at the point 
I have reached, and to bring forward my results, such as they 
are, without undertaking further investigation. 
The object of microscopic technique when applied to an 
organism such as a trypanosome is to produce a microscopic 
image which shall represent, so far as possible, the form and 
minute structure which we believe the organism to possess 
actually in the living state, true in all details, exact to a 
definite known scale of magnification, and coloured artificially 
so as to assist in rendering visible the different parts of the 
organism. A method which would have this ideal result 
would be a perfect method; but unfortunately no such 
method is known to exist, since all technique deforms or 
falsifies the form or structure of the organism to a greater or 
less extent. We are therefore confronted at the start with 
the difficulty, that since we can only arrive at a conception of 
the true and actual structure of the objects by the use of 
methods of technique, we are obliged to estimate the devia- 
tions from the truth, produced by technique, solely by a 
comparison of results which are themselves one and all 
defective. The only conceivable method by which the true 
form and structure of Trypanosoma lewisi could be 
recorded would be by a photograph of it in the living state; 
but I know of no method by which a snapshot can be taken of 
a minute and transparent organism, in a state of incessant and 
active movement, at a magnification of 2000 or 3000 diameters. 
It was necessary, therefore, to find at the outset some method 
of killmg and preserving the trypanosomes with the least 
possible deformation or alteration, in order to serve as a 
standard of comparison for other methods. It has always been 
my experience, and I think that of others, that in the case of 
Protozoa of larger size, such as Cilata, Amoeba, etc., the 
most life-like preparations can be obtained by simply exposing 
suddenly the living organisms, moving freely in a small drop 
of the medium they inhabit, to the vapour of strong osmic 
acid. The organisms are then examined without further 
