A technique has been devised for performing
inulin clearances in man, which is a great
simplification on the method used by earlier workers.
The simplification is threefold.
A single injection is used in lieu of a large
priming injection followed by a sustained infusion
to maintain the blood inulin concentration. As a
result of this the blood concentration is constantly
falling throughout the experiment, so that
some difficulty may be experienced in getting the
exact mean blood concentration for each observation.
Urine specimens were voided in the natural way,
and catherisation of the bladder followed by washing
out with saline was not practised. It was
felt that such a drastic procedure was not
warranted by a clinical experiment.
This is an obvious source of error on account
of large differences between blood and urine
concentration, but if the urine flow is kept at
a high level by giving the subject large quantities
of water to drink this can be minimised.
A marked improvement in the manner of
estimating blood inulin has been introduced.
This method is both simpler and of greater accuracy
than the original ones used in the estimation of
inulin. It is on account of the greater accuracy
that a relatively small single injection can be
This method is much simpler than a similar
one which has been introduced by Alving, Rubin and
Miller in America and which Is fairly generally
used in that country now. It is possible,
however,that their method may be of slightly
greater accuracy. I am sceptical of the
use of this method without removing the blood
glucose. The authors state that it is applicable
at blood concentrations of over 30 mg. /100 c.c.
The colour due to fructose in Herbert's
method is 88% developed after 15 minutes, and
this follows a rectilinear relationship. At this
time the colour due to glucose is negligible. By
the other method, however, the specimens are
incubated for 1 hour, and though the proportions
of the reagents are different, one feels that there
must be a considerable colour development due to
The results obtained in a series of subjects
by this method are analysed and discussed, and
certain of the observations are compared with
synchronous urea clearances.
In the course of these investigations the
distribution of inulin in the human body is also
studied, and the fact that inulin is excreted by
a simple physical process of filtration is
demonstrated by observations showing that the rate
of excretion increases proportionally to the blood
inulin concentration. As further proof of
filtration, it has also been shown that when the
fall of blood concentration is plotted logarithmically
against time, a rectilinear relationship