The record-union., 1899-10-16
MALARIA AND
MOSQUITOES.
Ronald Ross Demonstrates That the Insect Car
ries the Malaria Parasite

| to several days the parasites reach
their highest development within the
! vertebrate host, and become either (a)
| sporocytes or (b) gametocytes.
The sporocytes, which are produced
asexually, contain spores which vary
in number according to the species. The
spores do not possess any appreciable
cell-wall. When they are mature the
corpuscle which contains them bursts
and allows them to fall into the serum
They then attach themselves to fresh
| blood corpuscles, and continue the
| propagation of the parasites indefinite
! ly in the vertebrate host The residuum
of the sporocyte, consisting chiefly Of
the pigment, is taken up by the phag-
| ocytes of the host for eventual disposal
| in the host.
The gametocytes, while in the blood
! of the vertebrate host, are still con-
tanned in the shell of the corpuscle.
HOW DEVELOPED.
In some species their general form
| and appearance is very like that Of
/ the sporocytes before the spores are
! differentiated; in another, however,
they possess a special crescentic form.
| They continue to circulate in the blood
! for some days, or even weeks accord
ing to the species), without change;
| but when they are drawn into the ali
! mentary canal of certain suctorial in
/ sects, they undergo further develop
ment. In a few minutes after finding
! themselves in their new position, they
! break from the enclosing corpuscle by
! a kind of expansion, swell up slightly.
! and then commence their sexual func-
| tions The male gametocytes emit a
variable number Of Emergencies,
which escape into the serum of the in
| gested blood, leaving behind a residuum
consisting chiefly of pigment-as in the
! case Of the sporocytes. The individual
! microgametes are delicate but very ac-
tive filaments, consisting chiefly of
| chromatin, and sometimes seen to have
a slight swelling at one point of their
length-in the middle, when free, ac-
cording to my observations After es-
cape from the male gametocyte, the
| microgametes seek the female game
tocytes. which consist each of a single
I motionless macrogamete One micro
gamete now enters bodily into a macro-
gamete and fertilizes it, producing a
| zygote.
! FURTHER HISTORY.
The further history Of the zygote has
been traced, as regards three species
of this group of parasites, in certain
kinds of mosquitoes. After being fer
tilted, it acquires the power of escap-
ing the phagocytes of the ingested
blood which surround it, of working its
way through the mass of blood, of pass
ing through the thickness of the stom-
aeh (middle intestine) of the mosquito,
and of affixing itself to the outer sur
face Of the organ. Here the zygotes are
first found as oval cells about $40 u
in diameter. They still contain the
| granules of pigment which the macro-
gametes possessed before fertilization.
Growing rapidly, they soon acquire a
capsule, and begin to protrude into
| the body-cavity Of the mosquito. From
an early period the nucleus divides into
a number of pOrtions-zygotome
each containing a fragment of chroma-
tin. AS growth advances, the Zygoto-
meres become spherical blastophores.
bearing each a large number of deli
cate, filamentous zygotoblasts on their
external surface-each zygotoblast be-
ing affixed to the surface of the blasto-
phore by one extremity. AS maturity
is approached the zygote, though still
attached to the outer wall Of the in
sects stomach, protrudes freely into the
body cavity; it's pigment tends to dis
appear; and lastly, the blastophores
disappear leaving the capsule packed
with thousands of zygotoblasts. Ma
turity is reached in from one to three
weeks, according to the external tenn
perature, when the zygote reaches =
size Of 90 u or more. The capsule then
ruptures, pouring the zygotoblasts into
the insects blood.
THE ZYGOTOBLAsTS
The zygotoblasts are now seen to be
delicate fagellulae or mastigopods
with the chromatin and one or two un-
stained areas in the middle, and two
opposite tapering 1agella. have not
however, observed any notable move
ment in them, probably on account OF
the necessary dissecting medium. After
being discharged into the insects
blood, these bodies are carried away
by the current into all parts of the tis-
sues, and finally effect an entry into the
large grape-like cells Of the saliyarv
8Iand-especially tia cells of the short
middle lobe-where they accumulate in
very large numbers. From the cells
OF this gland they pass into the duct
, which runs TO the extremity of the mid.
die stylet, the lingula, and thence es-
cape during haustellation into the blood
OF new vertebrate host. Here. il nous1
be supposed, the fagenulae attack the
corpuscles and become the intra -cor-
puscular amoebulae with which we
started
FOUR POINTS TO NOTICE
Four points require notice. Q) There
are reasons for supposing that the
gametocytes are or may be produced
by the conjugation of two or more
/ amoebulae in one corpuscle. (2) The
gametocytes of several species show
after escape from the corpuscle. one o,
more minute spherical bodies attached
/ 10 their margin; which [ assume r.
= represent polar bodies 81 The voune
1 zygote of at least one species (ot
cfoWs) possesses, shortly after fertiliza.
2 ton, somewhat active powers of loco.
motlon. (D The mature zygotes of a.
e least two species often contain large
: Drown, thick-shelled, cylindrical bod.
les, the nature of which has NOT ve-
peen elucidated, and which NAV h,
parasitic fungi of the mosquito.
HOW THE FACTS WE'RE ASc,I,1