Omaha daily bee., 1919-05-18
of Infections by Insects.


There are a few infectious dis
eases. Of which malaria and yellow
fever are examples, in which the in
fictitious agents are exclusively con-
veyed by, insects. All such diseases
are due to animal parasites, which
for complete development require
two or more hosts, one Of which is
man. Each host nourishes the para
site during one phase of its growth
only, so that in order to reach ma
turity the latter must pass consec-
utiyely from one host to another.
Furthermore, since parasites are re-
strfcted to especial hosts, the pres
ence of an appropriate host for each
one is imperative If they are to be
perpetuated. Therefore it follows
that the communicability of a dis
ease Is only possible.,in the event of
the presence of that particular va
r1ety OF insect. So circumscribed is
the world of parasitism! AS exam
pies OF exclusive carriers we have
the mosquito, one variety of which
conveys yellow fever, another varie-
ty malaria. &
Ihe Body In Relation to Infections.
In previous papers we have con-
sidered the exacting conditions
which an infectious agent must full
fill to provoke disease. The fulfill
ment Of these conditions, however,
only meets the requirements in so
far as the micro organisms is con-
cerned, and therefore presents but
one side Of the problem; on the
other side. the position that the
body occupies in relation to infec-
tons Is equally important, and it is
to this phase Of the problem that
we turn.
In a previous paper this statement
was made: ut Is a matter of COM
mon observation that Of number of
individuals exposed to the same in
fictitious disease not all are attacked;
and in those susceptible, the disease
presents extraordinary variations as
regards its mildness or severity. If
the microbe were the sole factor
concerned, all exposed persons would
be attacked, and all taking the dis
ease would suffer to the same de-
gree; thing which everyone knows
never happens. Moreover, a per-
son may resist the action of a patho-
genie agent at one time, and fall
victim to it at another. The ques-
ton that naturally presents itself
Is, what brings about such radical
differences In the vulnerability of in
dividuals to infectious agents?" That
it is not always consequent upon
notifications in the agents, we know
from observation upon patients and
experiments upon animals. To ac-
count for it we are led to the con-
clusion that there is some subtle, diff
ference in the vital processes Of diff
ferent individuals, and in the same
person at different times.
Every healthy person is by nature
endowed with the means of combat
ing disease, but his natural defe..ses,
while they may be streng: ~sned,
may also be weakened by those
forces and influences which surround
him. Nor before the tribunal dis
ease are all men born equal, since
offspring constitutions defective in
defensive force. Furthermore, dur
ing the constructive Infancy and
childhood) and degenerative (old
age) periods of life the protective
forces are, one the one hand, weak
ened through immaturity, on the
other, by the fact that they are de-
Ginning with age. Therefore, to en-
vironment, heredity, and age, must
we look for an explanation Of any i'm
projections in our natural resistance
to disease.
Continued Next Sunday.)