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always been considered equal (note the exception in the Mery theory)
because that is the condition in the normal adult heart and because
of the necessity of this condition at birth. There appears, however,
to be no experimental evidence on the question. Accordingly, the
pig embryo was opened (see later) and a ligature slipped around the
heart at the auriculo-ventricular sulcus with the idea that if the
ligature was tightened at the completion of auricular systole, the
aortic-pulmonary and auriculo-ventricular orifices would be occluded
and the contents of the ventricles isolated. The experiment proved
successful in two out of ten trials. The heart was next removed
from the body, washed, the contents of each ventricle bled into
separate vials and the volumes compared. Comparison of the two
vials showed equal capacity as nearly as this rather primitive method
permitted in both cases. There being no valid objection to equal
ventricular capacity (generally accepted), the point was considered
as settled in the affirmative. The two ventricles in the living fetal
pig contain or at least expel equal quantities of blood.

II. The pressure exerted by the right and left ventricles in the
fetus has alsd been considered equal, because both ventricles expel
blood into the Aorta descendens, and secondly by observation, nicely
shown in Ziegenspeck's table, because the right and left ventricular
walls are equally well developed until after birth when the left
ventricle wall hypertrophies rapidly. Our later experiments required



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I



Course of the Blood Through the Fetal Heart, 93

the simultaneous recovery of blood under identical conditions and
to this end the following technique was employed:

Pieces of glass tubing about 10 cm. in length were carefully
drawn in the flame to a fine connecting piece of about 1 mm. in
diameter; laid aside to cool and then carefully broken at the point
indicated (Fig. 2). This procedure resulted in pipettes of the same



1
Fig. 2.

opening and, when fastened together with a small elastic band, per-
mitted sufficient spreading to allow the pipettes to be passed one
to either side of the ventricular septum and permitted their use as
a single pipette. The opening in the pipettes was small enough
to necessitate an actual pumping on the part of the ventricles,
while the capillary attraction aided in holding the contained
blood in place. This was further assisted by mouth pieces of rubber
tubing which were pinched off on the withdrawal of the pipettes from
the heart.

The beating heart was laid bare (see later) and the pipettes
thrust one into each ventricle simultaneously. In all cases where
the pipettes were properly introduced and where the heart continued
to beat, the blood mounted progressively and evenly in both ; proving
to our satisfaction that the pressure exerted by the right and left
sides is an equal one. Further there was little, if any, appreciable
oscillation of the blood in the two pipettes which went to show
that in the opened chest little aspirating action was manifested by
the ventricles. The results, thus far, are in perfect harmony with
what has been quite generally accepted and may be said to sub-
stantiate these views in an experimental way.

It was found that in the majority of pigs, the heart suffered but
little inconvenience through the introduction of the pipettes and in
some the heart beat quite rhythmically for many minutes even
after they were withdrawn. Inasmuch as it was impossible to
estimate how long it would take the blood to reach the heart from a
given point, a requirement was set that the heart must beat at least
five times after the introduction of the pipettes and that the blood



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94 Augustus Grote Pohlman.

must mount evenly and pix)gressively in both pipettes. Each pig
used therefore directly controlled the point that the ventricles exerted
an equal pressure.

Injection Experiments.

We have seen that the legitimate cry of artifact was raised by
Born to the anatomical findings of Ziegenspeck^ and that it may also
be raised to all injection experiments on the dead animal even if
the animal be used directly after death and all precautions taken
to avoid imdue pressure. The heart itself is no longer the active
agent and there is no way of determining how much the contracture
of the heart muscle may influence its normal intrinsic relations.

Technique. The following idea was carried out: to inject a non-
irritant granular substance suspended in normal salt solution into
a selected vein; to allow the blood current to propel these granules
to the heart; to recover some of the blood from both beating ven-
tricles under identical conditions; and to examine the blood re-
covered for the granules injected.

Stand was taken in the abattoir where the pig uteri were removed
and dropped into a tank truck. The larger and uninjured uteri
were selected and laid upon a table. Next a small incision was made
into the uterine wall at some distance from the markedly vascular
area and the incision widened by tearing to allow the escape of the
pig. It was found that tearing through the uterine wall practically
eliminated all hemorrhage and pigs were rejected if any amount
of oozing occurred.

Injection was made only in those pigs in which the cord pulsation
was strong. An ordinary hypodermic syringe was filled with corn-
starch granules suspended in normal salt solution, the air expelled,
and about one half of the syringe contents was injected slowly into
the imibilical vein, some 5 cm. from the navel. The needle with-
drawn, the pig was rapidly opened with a large blunt scissors by
cutting through the length of the sternum and by a lateral cut through
the abdominal wall just below the diaphragm. A blunt instrument
was selected with the idea of tearing rather than cutting through
the tissues and pigs were again rejected if anything further than



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Course of the Blood Through the Fetal Heart. 95

a slight oozing resulted from the incisions. Next the pericardium
was incised and the paired pipettes thrust simultaneously into the
two ventricles. An arbitrary requirement was established that the
heart must beat at least five times after the introduction of the
pipettes, giving a better chance of recovering the granules injected.
The blood in the pipettes was immediately expelled into paired
vials, marked right and left, containing a small quantity of half per
cent acetic acid. The vials corked and shaken thoroughly. Later
the vials were separated, and the contents diluted to an equal quan-
tity with dilute acetic acid. Each was shaken a given number of
times, and a small amoimt of fluid withdrawn by a pipette from the
central area of the vials. Samples from the right and left sides
were placed on one slide and compared under the microscope for
the number of starch granules.

Objections.

1. The death of the mother. It is well known that pigs will
live in the removed uterus for many hours after the death of the
mother. In pur experiments the time rarely exceeded half an hour
and in some cases about fifteen minutes after the sow's death.

2. The contraction of the uterus. This was not marked but was
present in some cases. We shall show later that this is not a serious
objection to our results.

3. The artificial factors introduced in opening the chest and
manipulating the heart. Granted present. The collapse of the
lungs especially offers an abnormal condition which probably limits
the pulmonary return.

4. The introduction of the pipettes. This is undoubtedly placing
the heart under some disadvantage, but we do not consider the ob-
jection a serious one because only a small quantity of blood was
withdrawn and because the heart showed no signs of interference
for at least five beats.

5. The introduction of a foreign substance in the circulation.
Cornstarch granules are non-irritant and non-toxic but are of suf-
ficent size to plug the capillaries, hence the blood was obtained as
soon as it reached the heart.



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96 Augustus Grote Pohlman.

It will be seen from these objections to our method that it is
practically impossible to reproduce the normal conditions in all
details as they are found in the fetus in utero. All that we claim
is that the artificial elements were avoided as far as facilities per-
mitted, and that our procedure is an improvement on experiments
made thus far. We at least allowed the blood stream to propel the
granules through what appears to be the normal course of the blood
in the fetal heart with a minimum of abnormal conditions imposed.
The method can, therefore, not be called exact enough for definite
proportions, and we make use of the term 'about equal' in this
paper as a personal equation set within 10 per cent of difference in
comparison of the two blood samples.

III. What is the course of the blood entering the heart through
the cava inferior ?

Injection of about one half of the contents of a hypodermic
syringe filled with a suspension of cornstarch granules in normal
salt solution was made into the umbilical vein about 5 cm. from the
naveL The pig was opened immediately, and the blood recovered
from the beating heart as in Experiment II. Seventeen paired
samples were recovered which registered equal coloration on dilution
to equal volumes, and these were examined. Five paired samples
proved negative — ^no com starch granules found in either ventricle
and twelve paired samples were positive — starch granules present
In all twelve paired samples the number of granules proved to be
'about equal' on both sides.

The experiment proves beyond a doubt (as far as pig is concerned)
that the von Haller-Sabatier theory is incorrect and that the ob-
jections of Williams, Peaslee and Macdonald were well taken. It
seems to prove that the blood from the inferior cava is distributed
about equally to the two ventricles, and is, therefore, in accordance
with the Wolff theory or with the theory of Galen-Harvey. The
former states that the blood from the inferior cava is split upon the
limbus Vieussens and that the foramen ovale does not afford com-
munication between the auricles; the latter assumes a small pul-
monary return, a mixing of the blood of the two cavro in the right
auricle, and a passage of mixed blood through the foramen ovale.



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Course of the Blood Through the Fetal Heart. 97

It now remained to inject the superior cava — ^for if the granules
did not pass through the foramen ovale, the Wolff theory was sus-
tained; while if the granules were recovered from both ventricles,
the theory of Galen-Harvey was substantiated.

IV. What is the course of the blood entering the heart through
the cava superior ?

This experiment was found more difficult than the preceding test.

It was found almost impossible to open the chest the full length

and expose the great veins at the root of the neck without injury to

these structures. The insult offered proved to be greater and the

death rate proportionately larger. Next only one or two drops

could be injected into the superior cava to avoid undue pressure, and,

when the needle was withdrawn, the unsupported vein tended to

bleed freely. The time limit was reduced to one to two seconds from

injection to introduction of the pipettes. Seven paired samples

were finally obtained which registered equal coloration on dilution.

One proved negative — ^no starch granules on either side, and six

positive — starch granules present. In four, the number of granules

on the right and left sides proved to be ^about equal ;' in one, more

were found on the left than on the right, and in one, more on one

side than on the other (labels confused). In both of these samples

the excess was easily 50 per cent.

The fact, however, that starch granules injected into the superior
cava did pass through the foramen ovale in all cases where they were
demonstrated at all showed conclusive evidence in favor of the theory
of Gralen-Harvey that the caval currents mix in the right auricle
and that mixed blood passes from the right auricle into the left
through the foramen ovale. Inasmuch as about ten seconds elapsed
from the injection of the umbilical vein to the recovery of blood from
the heart in Experiment III, and one to two seconds from the injection
of the superior cava, it was thought possible to make a double in-
jection in the same pig using colored granules in the one and color-
less granules in the other injection. If both varieties of granules
were found on both sides, the experiment would show that the cur-
rents mix in one and the same pig.
Pigs in this experiment were opened first and about ten seconds



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98 Augustus Grote Pohlman.

allowed from the injection of the umbilical vein with colored
granules (I-KI) to injection of the superior cava with colorless
granules. Only six pigs lived through the requirements in two full
mornings work, and of the six, three samples were lost owing to
the hurry. Two paired samples were obtained and one from the
left side (right pipette struck the septum). Superficial examination
of these samples revealed the presence of both varieties of granules
on both sides in the two and both varieties in the one from the left.
There was of necessity a delay in counting, and when it was at-
tempted some hours later, it was found that the iodine had diffused
and colored a large proportion of the colorless granules so that a
comparative count was impossible. The experiment, however, further
substantiated the Galen-Harvey theory and opposed, therefore, all
the more the Wolff theory.

The results from our experiment in the living embryo lead to
the following statement: that the ventricular capacity and pressure
is an equal one; that the foramen ovale does afford communication
between the two auricles; that the blood of the two cavsB mixes in
the right auricle ; and that mixed blood passes through the foramen
ovale. We agree, therefore, with the theory of Galen-Harvey and
believe to have established it through experimental evidence.

It now remains to consider what objections may be raised to our
results and wherein the evidence supports the Galen-Harvey theory
as opposed to all other theories.

It will be seen from our results in the living pig embryo that
about one half of the return through the superior and inferior cav»
passes through the foramen ovale into the left auricle. This fact
might be interpreted in one of two ways if we grant, as we must,
that the collapse of the lungs through opening the chest interferes
with the pulmonary circulation — ^the passage of blood through other
parts of the fetal body not necessarily being affected :

a. The pulmonary return is relatively free, as stated in the Wolff
theory, and that the artificial factors (collapse of lungs and manipula-
tion of the heart) are sufficient to practically prevent blood from
passing through the lungs ; or,

b. The lung circulation is relatively small in amount and that



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Course of the Blood Through the Fetal Heart. 91>

the pulmonary return is reduced by the artificial conditions so that
it might be well within the personal equation set in our experiments
(10 per cent).

The first interpretation offers a serious objection to our results
because those investigators favoring the Wolff theory will hold that
if we interfere with a large pulmonary return (about one half
[Wolff], exactly one half [Ziegenspeck] of the contents of the right
ventricle), we also destroy the normal balance of return to the
auricles through increase in flow through the cava inferior and
through decrease in flow through the pulmonary veins. Hence,
the normal position of limbus Vieussens to the orifice of the inferior
cava and the function of the foramen ovale may be rendered false.
This criticism we have foreseen and we, therefore, discuss the posi-
tion of the Wolff theory rather fully.

The results of our first two experiments have confirmed the major
premise of the Wolff theory that both ventricles expel the same
amount of blood under the same pressure, and we now come to an
examination of the physical laws underlying the flow of the blood
through the arteries. Ziegenspeck based his measurements on the
arguments that if the caliber of the ductus and Pars comm. aorts&
was an equal one, they transmitted equal quantities of blood; that
this quantity transmitted by each vessel was equal to one half of
the contents of a ventricle; and that the Aorta descendens carried
away one half of the contents of both ventricles. We stated in our
objections to these propositions that we believed it might be shown
that the ductus transmits more than the Pars comm. aortce ; and that
both feed into the Aorta descendens more than one half of the con-
tents of both ventricles.

If we can prove that the resistance to flow in the Pars comm.
aortffi and in the ductus is less than in the branches of the aortic
arch and in the right;^ and left pulmonary arteries respectively, then
we also prove that the Aorta descendens carries more blood than
the caliber of its lumen would indicate, while the other branches
convey relatively less. We believe we can substantiate the generally
accepted idea that the placental area is the point of least resistance
in the fetal circulation for the following reasons :



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100 Augustus Grote Pohlman.

1. The two large umbilical arteries feed into one large umbilical
vein — a proportion of lumina which would indicate that either the
arteries are under lower pressure than usual, or the vein is under
relatively higher pressure. In either case, it would present a low
resistance in the placental capillaries.

2. The umbilical vein, practically of round lumen, transmits
blood directly and indirectly into the intra-thoracic cava inferior
without any marked increase in lumen of the latter vessel, showing
that by far the larger proportion of blood passing down the Aorta
descendens is returned through the umbilical vein.

3. The umbilical arteries and vein have a long and tortuous
course through the jelly-like cord which probably offers little support
to the vessel walls, and were not the placental resistance lower than
the resistance in the vessels of the embryo body, little blood would
pass through the umbilical vessels, whereas we know the reverse
to be the case. It must be remembered that in human embryos the
cord usually averages about 55 cm. at birth, and that the umbilical
arteries may be reckoned on an average of 50 cm. longer than any
other arteries in the fetal body, and the vein, while not proportionately
long, is easily 40 cm. longer than any other vein. This distance of
a little less than a metre represents an appreciable amount in terms
of intrinsic vessel resistance. •

4. There can be but little doubt that the contraction of the uterus
must increase the resistance in the placental site and still the fetal
heart is able to force the blood through the long course and quite
freely. This is our answer to the objection that opening the uterus
rendered false the circulatory condition in the fetal pig.

6. Taking Ziegenspeck's measurements at their face value if
a 2.97 — ^mm. ductus and Pars comm. aortse feed into a 3.832 mm.
Aorta descendens, then the resistance in the latter vessel must be
considerably less than the resistance found in the lungs and carotid-
subclavian vessels, for the lumen is too small to carry off the blood.
It should read 4.14 + mm.

From these data we are able to assume with reasonable certainty
that the resistance to flow in the placental area must be considerably
less than in the fetal body, and that, therefore, until this resistance



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Course of the Blood Through the Fetal Heart 101

is a known quantity, the lumen of the Aorta descendens is no
criterion of its carrying capacity. We believe that the Aorta des-
cendens carries more than one half of the contents of both ventricles,
and believe this is not only a logical deduction but that it is con-
firmed by observation.

Conversely, if the circulation through the Aorta descendens is
relatively free, then the blood flow through the carotid-subclavian
and pulmonary arteries is relatively small. In other words, these
two systems return less than one half of the contents of both ven-
tricles. While this view is entirely contrary to Ziegenspeck's law of
the equal division of blood, it is not entirely contrary to the Wolff
theory of the splitting of the current of the inferior cava upon the
limbus Vieussens. It will be necessary to substantiate our evidence
from the injection experiments by an attempt to show clearly that
the lung circulation is relatively smaller in amount than the circula-
tion through the carotid-subclavian systems, or negatively, that the
ductus carries more blood than the Pars comm. aortCB. The two
points will be argued under separate headings, although they lead
to the same result.

Evidence that the circulation through the lungs is relatively small
in amount:

1. The histological appearance of the fetal lung, even when
hardened in situ, does not substantiate the theory that large quantities
of blood pass through the pulmonary circulation. The air sacs are
collapsed, the capillaries are compressed and tortuous and possibly
more numerous than elsewhere in the fetal body, l^ot only is the
blood current interfered with directly in the capillary system, but
the expansion of the vessels to the blood stream is limited.

2. The right and left pulmonary arteries are placed practically
at right angles to the blood impact, while the blood wave passing
aroimd the aortic arch meets the carotid-subclavian vessels with their
openings more nearly parallel to the current. Showing if the lumina
of these vessels read alike, the carotid-subclavian arteries wiU re-
ceive a trifle more blood (the grain of truth in the Sabatier theory).

Evidence that tKe ductus conveys more blood than Pars comm.
aortfiB and that it carries more than one half of the contents of the
right ventricle :



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102 Augustus Grote Pohlman.

1. The laws govering the equal flow of fluid through pipes
have certain limiting clauses ; not only must be the *head', the direct
resistance at the pipe opening and the pipe lumen and character be
the same, but the pipes must be of the same length and have the same
course. Therefore, the Pars comm. aortse will transmit less blood
than the ductus, even if the caliber be circular and of the same di-
ameter, because the course of the blood from the left ventxicle is a
longer one ; because the course is curved as opposed to the relatively
straight line to the ductus; and because the branches on the arch
are more advantageously placed to interfere with the current.

2. If in our experiments we interfered with a large flow of blood
through the lungs, then one of two things must have occurred :

(a) We increased the pressure on the right side in order to force
the excess of blood through the ductus, or

(6) We decreased the amount of blood expelled by the right
ventricle.
We have shown in our experiments that the pressure on the right
and left side continued to remain the same, for the blood mounted
progressively and equally in the pipettes when they were properly
introduced and where the heart continued to beat. Inasmuch as no
difference was observed in the character of the heart beat, we may
infer that lie ventricles continued to expel equal quantities of blood
as demonstrated in Experiment I under the artificial conditions
mentioned. If we grant that the lung circulation is free, the ductus
carried away the excess without any appreciable effort on the part
of the right ventricle; according to Ziegenspeck, the ductus would
have to carry double the amount, and according to Wolff perhaps
not quite double. If we grant that the circulation is relatively
small, the ductus carried but little more than normally.

We, therefore, do not see any evidence that we interfered seriously
with an alleged large amount of pulmonary return or that we over-
supplied the vena cava inferior with blood. Further, waiving all
this evidence aside, if we did increase the amount of return through
the inferior cava, we also raised the pressure in that vein, and we
still do not see why the limbus Vieussens should not divide the cur-
rent in the manner demanded by the Wolff theory. If we inter-



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Course of the Blood Through the Fetal Heart 103



Online LibraryAmerican Association of AnatomistsThe Anatomical record → online text (page 9 of 50)