52
Para.29
example, if the parasites are not numerous enough to be found, they are gener-
ally not numerous enough to produce fever.
As a rule, we seldom search more than two well-made specimens for the
organisms, and if we detect none in these we record the result as negative.
Thus, we may say that if the parasites number less than one in two speci-
mens they are below the vanishing point. As just said however, if they number
less than this on the average, at least in a case of quartan, they no longer cause
fever,—that is, they are also below the fever point. Hence, we may agree that
the vanishing point and the fever point coincide. The point of toleration is prob-
ably some way below the fever point, because we can imagine that the parasites
may still be numerous enough to evoke a certain amount of occult trouble in
the system although they may not be numerous enough to evoke actual fever.
Some figures will serve to fix those ideas. Suppose that a field of an oil
immersion lens suitable for searching for the organisms contains 500 corpus-
cles; and suppose that a well-made preparation of blood contains 100 such
fields. Then two specimens will contain 100,000 red corpuscles. Suppose
again that we take the fever point and the vanishing point to lie at one
parasite in two specimens; this will give one parasite to 100,000 corpuscles
at these points.
Now, the total amount of blood in a man is generally put at about 1/13 of
his body weight; a man of 130 lbs. weight will contain 10 lbs. of blood
[38, p. 54.], and 10 lbs. of blood contains about 25 billions of corpuscles
[38, p. 4.]. Hence, when standing exactly at the vanishing or fever points,
the parasites will still number as many as 250,000,000. That is, if they are
at all less numerous than this they will neither produce fever nor be found
on ordinary examination. In other words, they may exist in hundreds of
millions in the system without either causing fever or being readily detect-
able !
These figures may be commended to the attention of those hasty observers
who think that the parasites are absent in a case because they cannot detect
them on one or two examinations. Of course, the numbers given above are
only illustrative, and I know of no exact determinations on the point; but they
are near enough to the truth for my present purpose.
If we must search two specimens to detect one parasite when the parasites
number as many as 250,000,000, we must search more to detect one when
they are less numerous. Thus, if there be only 25,000,000 parasites, the
chances are that we must search 20 specimens (1,000,000 corpuscles) before
finding one—a labour of some hours; and 500 specimens must be searched
when there are only 1,000,000 parasites, and so on.
Yet it is obvious that a few hundred parasites would suffice to keep
alive the infection from day to day in a patient. But the chances against
our detecting one, when they exist in such small numbers, are enormous.
At the same time, if it requires 250,000,000 parasites to produce even slight
fever, it is clear that a few hundred are unlikely to have the least effect on
the host.
When the parasites are so few that they produce no appreciable effect,
we may conjecture that their number stands at or below the point of toleration.
In the case of halteridium the point of toleration is high—is above the vanish-
ing point. In proteosoma it is lower, sometimes above and sometimes below
the vanishing point. In human malaria it must be below the vanishing
point, because when we can find the parasites (exclusive of crescents) there
is almost always fever or illness.
Of course, all this must be admitted to be theory until someone undertakes
the necessary laborious studies. But it is a sounder theory than the one of
of encapsulation. There are no observations to support the latter; no encap-
sulated condition is required to explain the facts; and in halteridium we can
actually watch the continued propagation of the parasites occurring by means
of the ordinary sporulation process. At all events, the first theory gives
a wonderfully homogeneous picture of a continued malarial infection. Instead
of having to imagine periods of ordinary propagation, alternating with periods
of encapsulation, we are called upon to conceive for all kinds of malaria only
what we see in halteridium—a continued pervasion of the blood by the parasites
multiplying indefinitely in the usual manner.