6
in none of the specimens was it directly attached to this structure (Plate I, fig. 9 b, c, e and f),
The protrusion of the brush of filaments progresses rapidly and is seen in all stages from a
relatively short curved rod (Plate I, fig. 9 c, e and f) to the long fully developed wavy flagellum
measuring from 15μ to 20μ ( Plate II, fig. 1 a).
From a careful study of the formation of the flagellum 1 believe that it forms within a
vacuole and that the pink area seen when parasites are stained by Giemsa's method is due to
the deposition of colouring matter in the vacuole. The fact that after the extrusion of the
flagellum the vacuole collapses and then appears as a pink band on either side of the insertion
of the flagellum further suggests its relation to the flagellum, and I therefore propose adopting
t he name ' f l agel l ar vacuol e' gi ven i t by Lei s hman.
Many of the round or Oval parasites are seen in all the stages of flagellation while lying
side by side and in some the division of the macronucleus has already taken place (Plate I, fig.
9 , f ). In some of these parasites the flagellum was seen to end in an achromatic zone close to
the micronucleus and Plate II, fig . 1 a, shows a parasite in which the flagellum passes a little
beyond the micronucleus to end in a pink dot.
MacNeal1 6
w h o h a s s t u d i e d t h e a t t a c h m e n t o f t h e f l a g e l l u m o fT
r y p a n o s o m a l e w i s i
s t a t e s t h a t
in favourable specimens it can be traced to an achromatic space in close proximity to the
micronucleus ; Laveran and Mesnil1 have also noted this appearance in the same trypanosome.
Considerable variation is met with in the further stages of the first type of development
described. In many parasites, as has been mentioned above before flagellation has begun, the
macronucleus divides into two, and this is followed by the enlargement and division of the
micronucleus. Two flagellar vacuoles develop close to the micronuclei and in some cases
are seen fused together ; the two flagella rapidly pass out of them and as division proceeds the
flagellates are seen attached by their flagella alone (Plate II, fig. 1 c) or by both poles.
In other cases the parasites increase in size and become much vacuolated, the macronucleus
enlarges and shows signs of division while the micronucleus has already divided. Two
flagella now develop a little distance apart and later become extruded and on completion
of the division of the macronucleus the parasite splits longitudinally into two spindle-shaped
cells (Plate II, fig. 1 b). Some of the enlarged oval flagellates also showed signs of elongating
into these spindle-shaped forms (Plate II, fig. 1 a and c).
It will thus be seen that a certain percentage of the developing parasites pass on to
flagellation and then divide longitudinally to form oval or spindle-shaped flagellates, there
being no regularity observed in. this process.
In the second type, development which results in the formation of rosettes consisting
.of from four to eight flagellates also follows on the early enlargement of the parasites.
The macro- and micro-nuclei divide and pass to the opposite sides of the cell (Plate I, fig.
10), which has a globular appearance and is rich in granular protoplasm. One of these macro-
nuclei divides again while the other may as yet remain unchanged or only show an increase
in size ; but the micronuclei during this time divide rapidly so that while there may be only two
macronuclei, there may be three or more micronuclei (Plate I, fig . 10 e), Fig. 10 d and f shows
the method of division of the micronucleus ; after it has become thickened and considerably
elongated it divides transversely into two, a method of division which is maintained throughout
all the later stages of the development.
The division of the macro- and micro-nuclei and the further growth of the cell result in
the formation of a body measuring from 10,u, to 12 μ in diameter ; its protoplasm stains reddish
blue with Giemsa's stain and contains groups of vacuoles (Plate I, fig. 10). Such a cell may
contain from four to eight macro-and micro-nuclei grouped about its centre. The flagellar
vacuoles now develop close to the micronuclei and later all the flagella pass out from one side
of the cell (Plate II, fig. 1 d and e). Separation of the flagellates now begins at the flagellar
e n d a n d t r a n s p a r e n t l i n e s p a s s u p t h r o u g h t h e c e l l , a n d f r o m f o u r t o e i g h t f u l l y d e v e l o p e d
flagellates become separated and swim away.
These flagellates vary from 6μ to 12μ in length and from 4 μ to 5μ in breadth, their size
depending on the rapidity with which the rosette breaks up ; the majority are elongated and it
is from further growth of these that the long free swimming forms are produced. It is
important to note that equal longitudinal division of these flagellates while still attached or
when free was not observed.
Plate II, fig. 3 c, shows a rosette in the process of division ; the macronuclei are seen in
the two parts undergoing further division, while distributed along the sides and periphery of
the cell there are eight micronuclei and six flagella. Such a cell, it could be readily understood,
might produce even more than eight flagellates. Plate II, fig. 3 b, also shows a small rosette
of four elongated flagellates and two cells which have become separated from a rosette
containing six parasites.
The oval or spindle-shaped parasites which are formed either from the round flagellates or
from their further division exhibit very characteristic appearances. When stained deeply by
Giemsa's stain they contain dark blue granular protoplasm and a number of vacuoles of varying
size ; their macronuclei, usually circular in shape and situated about the centre, stain deeply