' 
1909. } BLOOD-PARASITES OF FRESHWATER FISHES. 21 
extracted, as in one of my preparations, the colour comes out of 
everything except the kinetonucleus; when the extraction has 
not gone quite so far, the karyosome of the trophonucleus also 
retains the black colour. The granulations of the cytoplasm are 
not, in my opinion, to be regarded as chromidia, since they give 
up the stain very readily, while the true chromatic structures 
retain it very tenaciously. 
Franga has drawn attention to the peculiar structure of the 
nucleus in the variety magna of this trypanosome. He writes: 
“hes moval, ses. « s'éloigne par sa structure de celui de presque 
tous les Trypanosomes. Au sein d’une substance incolore on voit 
la chromatine formant d’ordinaire deux parties bien distincteés ; un 
arama OLOCE eae. dun rouge vif, situé dans la partie du noyau 
la plus rapprochée du blepharoplaste; et un grand nombre de 
granulations petites et réguliéres, ou un reticulum chromatique, 
vers le coté du flagelle. Dans quelques parasites, plus rares, on 
ne voit pas le grand bloc de chromatine et alors il existe dans 
la substance nucléaire incolore une série de granulations dis- 
posées de fagon 4 former un cordon plus au moins sinueux.” “ Au 
contraire de ce qui existe dans le noyau des Trypanosomes de la 
var. magna, dans ceux de la var. parva il n’y a pas une distinction 
nette entre les portions chromatique et achromatique.” 
Franga’s observations appear to have been made on trypanosomes 
stained by the Romanowsky method, and my preparations coloured 
with Giemsa’s stain confirm his statements, But I do not believe 
it is possible to get a coherent or intelligible idea of the structure 
of the nucleus with this method of staining. My preparations 
stained with iron-hematoxylin show appearances quite different 
from those seen after use of the Romanowsky stain, and at the 
same time permit of a uniform interpretation of the structural 
details. The nucleus appears very much smaller and more 
compact after iron-hematoxylin than after the Romanowsky 
stain; and while it is possible that there is a certain amount of 
shrinkage by the former method, [ think there is certainly a 
considerable amount of artificial expansion and deformation con- 
sequent on the process of drying by the ordinary method of 
applying the Romanowsky stain. 
In never-dried preparations stained with iron-hematoxylin, the 
smallest trypanosomes (figs. 78, 79) show the nucleus as a clear 
oval space with a distinct limiting membrane, containing 
sharply defined karyosome of elongate-oval form. The karyosome 
is far from filiing up the entire nuclear space, which appears clear 
or shows very minute granulations. A nucleus of this type of 
structure may be found even in trypanosomes of large size 
(fig. 87), but the karyosome in such specimens is considerably 
larger and fills up nearly the whole nuclear cavity. Asa rule, 
however, in trypanosomes only slightly larger than the smallest 
that can be found (figs. 80, 81), the karyosome is seen to have 
budded off from one extremity, usually from that furthest from 
the kinetonucleus, a smaller part. This is the type of nucleus 
