THE STRUCTURE OF TRYPANOSOMA LEWISI. 779 
(2) Heidenhain’s iron-hematoxylin.—Feor this stain 
I make use of 3} per ceut. solution of iron-alum in distilled 
water and } per cent. solution of hematoxylin, which is made 
up as follows: A stock solution is made in the proportions of 
1 gramme hematoxylin, 10 c.c. absolute alcohol, 90 c.c. dis- 
tilled water; for use the stock solution is mixed with an 
equal volume of distilled water. 
In agreement with Schaudinn (1902, p. 190), I found it 
necessary to let the mordant and stain act for a long time. 
My procedure is as follows: Films, however fixed, are brought 
into absolute alcohol and kept there for an hour or so, then 
brought down through a series of grades of alcohol, differing 
by 10 per cent. between two consecutive grades, into distilled 
water, thence into the iron-alum solution, in which they are 
left till the next morning. The films are then dipped for an 
instant into distilled water, transferred to the hematoxylin 
solution, and left for at least twenty-four hours. [use both the 
iron-alum and hematoxylin solution in the solid watch-glasses 
mentioned above, taking care that none of the solution, in 
either case, gets on to the clean upper surface of the cover- 
shp. 
The important part of the whole method is the process of 
extraction of the stain. After being in the hematoxylin 
the film is washed with distilled water and placed in the 
iron-alum solution; in a short time clouds of colour can 
be seen coming out, especially if the coverslip be gently 
moved; it is then taken from the iron-alum and placed in tap- 
water, which stops the process of extraction. JI now examine 
the film, in tap-water in a -watch-glass, with a dry lens (Zeiss 
D with oc. 4). If the karyosomes of the trypanosomes can be 
seen clearly the extraction is sufficient, if not the film is put 
back again into the iron-alum for a short time, and the 
process of extraction and examination repeated. When the 
extraction is judged to be sufficient, the films are washed for 
twenty minutes in a current of tap-water, which is easily done 
by letting them float on the surface of the water in a beaker 
through which a gentle current of water is passed from a 
