A 
MONOGRAPH 
ON THE 
FfflTAL CIRCULATION. 
WITH THREE ILLUSTRATIONS OX WOOD. 
BY E. K. PEASLEE, A. AL, MJ)., 
PROFESSOR OF ANATOMY' JN DARTMOUTH COLLEGE AND IN HIE 
NEW YORK MEDICAL COLLEGE, AND OF SURGERY' 
IN THE MEDICAL SCHOOL OF MAINE. 
FROM THE AMERICAN MEDICAL MONTHLY, 
.wG»ip. 
NEW Y O R K : 
BAKER. GODWIN & CO.. BOOK AND .l< >B PRINTERS, 
CORNER NASSAU AND SPRUCE STREETS. 
1854. A MONOGRAPH 
ON THE 
F(ETAL CIRCULATION. 
BY 
E. R. PEASLEE, A. M., M. D., 
PROF. OF ANATOMY IN DARTMOUTH COLLEGE AND IN THE NEW YORK MEDICAL COLLEGE, AND 
OF SURGERY IN THE MEDICAL SCHOOL OF MAINE. 
[From the American Medical Monthly, May, 1854.] 
Fcetal Anatomy has, for several years past, received a large share of 
attention, while foetal physiology has hitherto been, to a great extent, neg- 
lected, except so far as mere development is concerned. It is, indeed, a 
department of no ordinary difficulty, since the human foetus passes through 
various successive phases of function, as well as development. In regard to 
its circulation, for example, it is at one time analogous to a fish; subsequent! y 
to a reptile; and does not become a true mammal, indeed, till after birth. 
Still, we may now enter this field with views somewhat extended; and 
it is the object of this paper to show that the view of the fcetal circulation, 
which is adopted by the highest authorities, is unsatisfactory and incorrect; 
and to propose such a view as the present state of science demands. 
In this new the last half of foetal life alone is included ; and it is proper 
to commence with a statement of the ideas, both in regard to the course and 
to the physiology of the foetal circulation, which are generally entertained. 
I. The course of the Foetal Circulation. 
About 150 years ago a violent controversy arose in France, and extended 
to the neighboring kingdoms, respecting the manner in which the blood passes 
between the auricles, through the foramen ovale.* It was excited by Meri's 
* For the arguments adduced in this controversy, see Senac's Traite de la Struc- 
ture du Coeur, tome 1, p. 369; and the Supplement, in tome 2. 2 
theory-that it passes from the left to the right auricle-while Harvey had 
assigned to the current an opposite direction. Boerhaave, Lancisi, Wins- 
low, and others, investigated the subject; and their conclusions have under- 
gone but slight modifications up to the present time. 
The course of the foetal circulation as usually stated-independently of 
the inferences generally associated with the facts-is as follows: 
1. The aerated, or arterial, blood returned by the umbilical vein, from 
the placenta through the umbilicus, and to the inferior surface of the liver, 
is thence poured into the inferior vena cava; a part having entered that 
vessel at once through the ductus venosus,* and the rest having first been 
transmitted through the liver. 
2. The blood in the inferior vena cava is poured into the right auricle, 
and by the Eustachian valve turned across into the left auricle through the 
foramen ovale. 
3. While the left ventricle is thus filled, the right is filled by venous 
blood, from the superior vena cava. 
4. The mostly arterial blood is sent from the left auricle through the 
left ventricle into the aorta, and principally through the branches from its 
arch to the head and upper extremities; the venous blood in the right 
auricle is sent through the right ventricle into the trunk of the pulmonary 
artery; thence in very slight degree to the collapsed lungs, but almost 
entirely through the ductus arteriosus into the descending aorta-there to 
mingle with the purer blood which has passed down through the arch of 
the aorta. 5. This mixed blood is distributed to all the parts supplied in 
the adult by the descending aorta; and the blood thus carried to all parts 
below the diaphragm is returned to the right auricle by the inferior vena 
cava. 6. But the internal iliac arteries are not only distributed in the foetus 
as in the adult. They are also prolonged on each side of the bladder, and 
above it to the umbilicus, and through the latter into the cord, and to 
the placenta. These prolongations are called the " umbilical arteriesand 
by them the blood is returned from the foetus to the placenta. 
This view is illustrated by Fig. 1, here taken from Carpenter's Physio- 
logy ; and which is placed on another page for the sake of contrasting it 
with the correct representation of the parts in Fig. 2. Some of the words 
in the preceding paragraph are also italicized, since they convey incorrect 
or false ideas, and will be particularly remarked upon in another connec- 
tion. 
II. The Physiology of the Foetal Circulation, as at present understood. 
1. The blood arriving in the inferior cava from the umbilical artery, 
"having been thus transmitted through the two great depurating organs- 
* This vessel extends from the umbilical vein directly into the vena cava. 3 
the placenta and the fan tai liver-is in the condition of arterial blood; but 
being mixed in the vessels (the inferior cava) with that which has been 
returned from the trunk and lower extremities, it loses this character in 
some degree, by the time that it arrives at the heart."-Carpenter's Human 
Physiol., 4 Ed., p. 997. 
2. This mixed blood is prevented, "in great degree, if not entirely" 
from farther admixture with the venous blood in the right auricle, by the 
peculiar action of the Eustachian valve ; which carries it at once through 
the foramen ovale into the left auricle.-Ditto. 
3. The ventricles contracting, the left propels its " arterial " blood into 
the ascending aorta, and supplies the head and upper extremities before 
undergoing any admixture ; while the right ventricle sends its venous blood 
through the (trunk of the) pulmonary artery, and the ductus arteriosus, into 
the descending aorta, there to mingle with the pure blood just mentioned, 
and be distributed to the trunk and lower extremities.-Ditto. 
4. " Thus the head and superior extremities, whose development is 
required to be in advance of that of the lower, are supplied with blood 
nearly as pure as that from the placentaand vice versa as to the rest of 
the body.-Ditto, and Wilson's Human Anatomy, p. 555. 
5. " In the adult the blood would be circulated through the lungs and 
oxydated; but in the foetus the lungs are solid and almost impervious. 
Only a small quantity of the blood passes, therefore, into the lungs; the 
greater part rushing through the ductus arteriosus," &c.-Wilson, ut sup., 
p. 553. 
6. "The pure blood from the placenta is distributed in considerable 
quantity to the liver, before entering the general circulation. Hence, the 
abundant nutrition of that organ, and its enormous size in comparison with 
other viscera," in the foetus.-Ditto. 
We find essentially the same statements in all the best authors of the 
present time; and, therefore, no farther quotations or authorities are deemed 
necessary. We have here, also, italicized such expressions as need particu- 
lar consideration, on account of their entire or partial incorrectness. 
Each of the preceding six propositions will be separately reviewed, with 
the intention of showing their incorrectness, and at the same time of demon- 
strating the only true view of the subject. A few remarks will, however, be 
premised in this connection, expressive of the author's doubts as to the pecu- 
liar-and really incredible-action universally assigned to the Eustachian 
valve. 
The assumed function of the Eustachian valve not probable. 
Some experiments, intended to elucidate this subject, and to which a 
great deal of importance seems to have been attached, were performed by 4 
the late Dr. John Reid.* The following was regarded as the most satis- 
factory : Having injected both the venae cavae, of a foetus of seven months, 
at the same time-the superior cava with yellow, and the inferior with red, 
injection-he found that the " red had passed through the foramen ovale, 
and filled the left side of the heart without any intermixture with the yel- 
low, except very slightly at the posterior part of the right auricle. Not a 
drop of the yellow appeared to have accompanied the red into the left side 
of the heart. From the left side it (the red) ascended the aorta and filled 
all the large vessels going to the head and upper extremities. The injection 
in all these vessels had not the slightest tinge of yellow." 
The yellow " filled the right auricle, free from admixture, except slightly 
at the posterior part of the auricle, as already mentioned. From the right 
auricle it filled the right ventricle, passed along the pulmonary artery, and 
filled the ductus arteriosus and branches, going to the lungs. On entering 
the aorta it passed down that vessel, filling it completely, without any 
admixture of red ; and thus, all the branches of the thoracic and abdominal 
aorta were filled with yellow. The whole of the red had passed to the upper 
part of the body," &c. 
Dr. Reid's experiments have, however, entirely failed to convince us that 
the Eustachian valve does, or can, turn the current of blood from the inferior 
vena cava, across the right auricle, and through the foramen ovale, into the 
left auricle, without admixture with the venous blood from the inferior 
cava. 
It is to be remarked, in the first place, that the complete isolation of the 
red and the yellow injections occurred only once in three similar experi- 
ments, and then in a foetus of seven months, the others being of four months, 
and at full term. Dr. Reid accounts for failure in the last case, since " the 
Eustachian valve is supposed to be less perfect at the full time than at an 
earlier period." What Dr. R. supposed, is really the fact, but would it be 
so, if the valve perform the part assigned to it ? On the contrary, we should 
suppose the necessity for the separation of the venous from the arterial blood 
would increase (if such necessity at any time exists) as the foetus becomes 
farther developed; and, therefore, that the valve w'ould be most perfect just 
at the very end of intra-uterine life. It will, however, be shown that no 
such necessity actually exists at any time during foetal existence. 
Again, we cannot suppose two currents of injection, forced through the 
vense cavse of a dead foetus, would comport themselves precisely as would 
the two currents of blood during life; even were the heart a passive organ. 
But when we consider its cavities, as exerting both a forcing and a suction 
power, the difference is vastly increased. In this view, the experiment 
* Edinburgh Med. and Surgical Journal, Vol. 43, p. 11, <fcc. 5 
appears utterly valueless, therefore. But if we are still inclined to regard 
the result as reliable, then it proves altogether too much-such a perfect 
non-admixture of the two currents during life being altogether inconceiv- 
able. 
A distinguished anatomist remarks, in regard to the assumed crossing of 
the two blood-currents in the right auricle, without intermixture: " how this 
crossing is affected, the theorist will wonder; not so the practical anatomist."* 
He then speaks of the direction of entrance of the two venae cavse, of the 
opening of the inferior almost directly into the left auricle; and of the use 
of the Eustachian valve-as enabling the anatomist at once to perceive the 
correctness of this theory. We confess, that, in our own case, the theory is 
more satisfactory without the anatomy than with it. Or, perhaps, we should 
rather say, that if our mere anatomy admits the belief in such a non-admix- 
ture in a dead foetus, our physiology will not for a moment, in a living one. 
And if there is an admixture, the assumed function of the Eustachian valve 
must be relinquished and another be assigned to it, if possible. 
On merely anatomical grounds, the anterior termination in the auricle 
of the superior cava may be regarded as necessitated by the relations of its 
primitive branches, and, therefore, of its trunk; the former being in front of 
the arteries rising from the arch of the aorta, while the termination farther 
back in the auricle of the inferior vena cava is demanded, by the liver being 
in front of it. Thus, also, its termination in the right auricle, so near the 
foramen ovale, may be necessitated by its relations to the aorta, and to the 
middle line of the trunk before perforating the auricle; and, therefore, the 
Eustachian valve may be considered as having a more important relation to 
the opening of this same vein, and the passage of blood through it, than to 
the circulation through the foramen ovale-tTiough it may incidentally 
exert some influence on the latter. 
These suggestions, be it observed, are made on merely anatomical 
grounds. They are made to meet the inferences just objected to, and to 
show that the latter alone cannot form a reliable basis for the physiology 
of the foetal circulation. Other facts, however, will be adduced in favor of 
the inferences just made; and the anatomy itself will receive some impor- 
tant corrections as we proceed. Meantime, we will regard the assumed 
function of the Eustachian valve as not proved, and as improbable. 
Objections to the physiological views generally entertained. 
1. No importance is attached to the fact that most of the blood from 
the placenta circulates directly through the liver ; except so far as its influ- 
ence upon the development of the liver itself is concerned, and so far as the 
* Wilson's Anatomy, p. 554. 6 
liver is a depurating organ. Indeed, it is incorrectly assumed, that the 
major part of the blood passes through the ductus venosus into the vena 
cava inferior. 
2. The fact that venous blood is returned from the lungs through the 
pulmonary veins to the left auricle, is entirely overlooked ; it being assumed, 
also, that almost no blood enters the lungs at all,-since, 
3. It is incorrectly stated that almost all the blood in the trunk of the 
pulmonary artery passes into the descending aorta through the ductus 
arteriosus. 
4. No stress is put upon the dilatation or the contraction of the auricles, 
as having any influence in mixing the blood contained in the two auricles, 
through the foramen ovale. 
5. It is assumed that the greater development of the head and upper 
extremities at birth, is owing to their having received a very pure blood 
during foetal life; and greatly different in this respect from that sent to the 
trunk and lower extremities. 
The validity of these objections, and others hereafter to be suggested, 
will appear in a subsequent part of this paper. Some remarks, however, in 
regard to the relative size of the ductus venosus and the umbilical vein, and 
of the ductus arteriosus and pulmonary artery, are proper in this connection. 
I. Relative size of ductus venosus and umbilical vein. 
To settle this question, I carefully dissected foetuses of from six months to 
eight and a half months. They were not injected, from the fact that injection 
passes more easily through the ductus than through the liver, in the dead 
foetus; and, therefore, the former becomes enormously distended, while the 
umbilical veins, and especially those in the substance of the liver, are less so. 
Hence it is impossible, in this way, to get a true idea of the relative size of 
these vessels. I have an injected foetus at full term, in which the ductus 
venosus is inch (.22) in diameter, but contracting to inch (.1) just 
before entering the vena cava; while the umbilical vein is only inch 
(.25) in diameter, and the inferior cava is considerably smaller than the 
ductus. Each umbilical artery, moreover, is as large as the aorta actually 
is in the living foetus at full term. It is from such exaggerations that we 
have heretofore acquired our ideas of the relative size of these vessels. 
To avoid this source of error, I carefully dissected these vessels, and com- 
pletely emptying them, laid them in their collapsed state upon a plane surface, 
expanded to their fullest width by the required manipulations and pressure. 
The width thus obtained equals the semi-circumference, or y of the diam- 
eter. The results are not absolutely accurate, for reasons at once apparent. 
But when vessels of the same structure are thus compared (as veins with 7 
veins and arteries with arteries), the relative size is thus more nearly obtained 
than in any other way which has occurred to me. 
In a foetus of about eight and a half months, I found the ductus venosus 
to have a semi-circumference of less than Tf, inch (.05); and the umbilical 
vein of A/o inch (-15). In a foetus of six months, the former had a semi- 
circumference of inch (.04), and the latter, of inch (.12)-the pro- 
portion being about one to three in both cases. Each of the three hepatic 
veins is quite as large as the ductus venosus; and these, with the latter, 
carry into the vena cava inferior all the blood brought from the placenta by 
the umbilical vein, and from the formative branches of the vena portae. 
(Fig. 2d, 7.) Admitting that one of the hepatic veins is sufficient to trans- 
mit the last mentioned blood (and the small size of the vena portae before 
entering the liver warrants this supposition) we have two hepatic veins and 
the somewhat smaller ductus venosus, to transmit to the vena cava all the 
blood from the placenta; and can perceive no adequate reason why the 
ductus should transmit more than one-third of that blood. Anatomy leads to 
this inference; though anatomical experiments-injected preparations-have 
led to a different conclusion. We consider the former far the more reliable. 
In the adult, the blood passes through the pulmonary artery and its branches, 
and through the capillaries of the lungs, and thence through the pulmonary 
veins into the left auricle-just as rapidly as it passes through the aorta, 
and just as rapidly as it could pass through the trunk of the pulmonary 
artery if it terminated at once in the aorta. Probably the same obtains in the 
case of the foetal liver. The living blood passes rapidly through its capilla- 
ries, because nutrient changes are there going on ; while an injection is first 
stopped by these minute vessels, then flows back through the large trunks 
to distend them, and finally distends to the utmost, the ductus venosus; 
and thus at last finds its way almost entirely through this passage into the 
inferior vena cava and the right auricle. 
Therefore, it is believed to be within the limits of truth to say that not 
over one-third, at most, of the blood returned from the placenta through the 
umbilical vein, is carried into the inferior vena cava by the ductus venosus. 
II. Relative size of ductus arteriosus and pulmonary arteries. 
In a foetus of six months, I found the semi-circumference of the pulmo- 
nary artery, before its division, to be y'/j- (.12) of an inch; and that of the 
ductus arteriosus, (-04). In a foetus of eight and a half months, the 
semi-circumference of the pulmonary artery was (-25) inch ; and of the 
ductus arteriosus, (.08) inch. In both cases the ductus was perceptibly 
smaller than either of the two branches of the pulmonary artery, sent to the 
lungs. In the older foetus it was also somewhat smaller than either carotid 
artery ; in the youngest I omitted to notice this comparison. In these cases, 8 
I measured the vessels in a collapsed state, as before described. The ductus 
tapered towards its distal extremity, in the older foetus; and was somewhat 
smaller at its union with the descending aorta, than the dimensions above 
given. 
The anatomical inference is, therefore, that the ductus arteriosus does 
not transmit any more blood into the descending aorta than each branch of 
the pulmonary artery carries to its lung. If it be remarked that the blood 
may rush more rapidly through the ductus than through the pulmonary 
arteries, and therefore a greater quantity be discharged, I reply that it can- 
not be transmitted in a current more rapid than that in the descending 
aorta, with which it blends; and as the latter cannot be more rapid than 
that in the main trunk of the pulmonary artery (since the latter and the 
aorta, at their commencement, transmit the same amount of blood, as nearly 
as may be), it follows that the current through the ductus is not more rapid 
than that through the pulmonary artery; and the ductus being one of its 
three branches, it is doubtless far less so. But, it will be remembered, that 
the two branches of the pulmonary artery, in the adult, transmit as much 
blood as the aorta, and, of course, with a rapid motion. Is there any 
assignable reason why the rapidity is not as great in the lungs of the foetus 
as in the adult ? or, therefore, why they will not transmit as much blood, in 
proportion to their capacity, and thus carry two-thirds of that received by 
the pulmonary trunk, while the ductus arteriosus receives but one-third of 
the same ? We think not. But if it should hereafter be proved that the 
ductus carries even one-half of the blood in the pulmonary trunk, into the 
descending aorta, from having a more rapid current than the two pulmo- 
nary branches, the relative size of the ductus and the pulmonary artery 
remains as before stated; and it will appear that the physiology of the cir- 
culation is the same, whether the proportion is greater or less within these 
limits. 
The relative size of the umbilical arteries is also greatly exaggerated in 
injected preparations. Each of these is actually a little more than one-half 
the diameter of the umbilical vein; and once and one-half the diameter of 
the external iliac artery; still being hardly larger than the carotids. When, 
therefore, we consider how many branches have been previously given off, 
from the arch to the descending aorta, it cannot be supposed that more than 
one-fourth, and probably not over one-eighth, of all the blood sent by the 
left ventricle into the aorta, can be by them returned to the placenta. Only 
the same amount is, of course, returned from the latter by the umbilical 
vein; and the mistake of supposing all the blood of the foetus to be trans- 
mitted rapidly through the placenta, as that of the adult is through the 
lungs, is thus corrected ; for the foetus has a reptile circulation. 
The accompanying figures will explain the preceding statements. 9 
Fig. I.-Diagram representing the anatomy and physiology of the foetal circu- 
lation-from Carpenter, and Wilson. The numbers represent the same parts as those 
in the next figure. 
Fig. II.-Illustrating the anatomy and physiology of the fcetal circulation-as 
demonstrated by the writer's dissections. 
Fig. I. 
Fig. II. 
1-The umbilical cord, with its vein and two arteries, proceeding from 2, the 
placenta. 3-The umbilical vein, giving off, 4, 4, two principal branches entering 
7, the vena portae; and a third, 5, the ductus venosus (here of its natural size, as 
compared with 3 and 4), which enters 6, the inferior vena cava. V-The hepatic 
veins receiving all the blood carried into the liver by 4, and 7; and discharging it 
into the inferior vena cava above the ductus venosus. The three branches generally 
terminate separately in the vena cava. 6-The inferior vena cava. 7-Formative 
branches of vena porta?, from alimentary canal, Ac. 8-The right auricle; the arrow 
indicating the course of the blood thence into 9, the left auricle. 10-The left ven- 
tricle. 11-The aorta. 12, 13-Arrows, showing the return of blood from the head 
and. superior extremities to 14, the superior vena cava; and thence into 8, the right 
auricle, and 15, the right ventricle; and, in the course of the bent arrow, from the 
latter into 16, the pulmonary artery. 17-The ductus arteriosus (actual size) termi- 
nating in 18, 18, the descending aorta. 19-The umbilical arteries (continuations of 
the internal iliac, and larger than the external iliac) returning a part of the blood in 
the descending aorta to 2, the placenta. 20-The external iliac arteries, distributed 
to the lower extremities ; the arrows at their extremities show the return of venous 
blood, by the iliac veins, to the inferior vena cava. 21-The remaining branches of 
the internal iliac (besides the umbilical arteries), and which are distributed, as in the 
adult, to the organs in the pelvis, Ac. 10 
Fig. 1st is taken from Carpenter's Physiology, and is here introduced for the 
sake of contrast with the correct representation. Fig. 2d shows the relative 
size of the ductus venosus and umbilical vein; of the ductus arteriosus and 
the pulmonary arteries; and of the umbilical arteries and umbilical veins, 
&c. It also shows the trunks of the hepatic veins, hitherto omitted; and 
some branches of the internal iliac, to the pelvis. 
I shall now proceed to examine particularly each of the six physiolog- 
ical propositions which have been given as embodying the received view of 
the foetal circulation ; in the course of which examination still other objec- 
tions to this view will be suggested; and, finally, such conclusions will be 
deduced as the present state of physiological science demands. 
Examination of the received view of the Physiology of the Foetal Circulation. 
In this examination I shall separately discuss the six propositions on 
pages 2 and 3, and will refer the reader to those pages to avoid repe- 
tition here. The passages which are italicized will demand a particular 
notice. . 
Proposition 1st.-Doubtless the placenta is a " (depurating" organ, in 
its influence upon the blood of the foetus : i. e., the blood, while traversing 
its minutest vessels, parts with some of its carbonic acid gas, and receives 
instead, from the mother's blood circulating in the maternal portion of the 
placenta, an amount of oxygen gas. Thus the blood becomes aerated, and 
in the adult would properly be termed arterial blood. This pure blood is, 
however, not found unmixed in the arteries of the foetus as it is in the adult, 
and therefore I shall term it instead, placental blood, to avoid all misunder- 
standing. The arterial blood, i. e., the blood in the arteries of the foetus, is 
a mixture of placental and venous blood, as will be shown. 
But of the pure placental blood, not more than one-third, as has been seen, 
at once enters the inferior vena cava through the ductus venosus; the remain- 
ing two-thirds, or more, being distributed to the liver through the vena 
portae. The former one-third, blending with the venous blood in the 
inferior vena cava (at least two or three times as much in quantity) is then 
carried as mixed blood (venous and placental, and probably considerably 
more than two-thirds venous') into the right auricle, where we leave it for 
the present. The remaining two-thirds of placental blood are, 1st, blended 11 
with the venous blood brought to the liver from the formative branches of 
the vena portae (fig. 2-7), which may be equal to one-third the placental 
blood in the vena portae; and thus this also becomes mixed blood, and 
three-fourths placental. But from this mixed blood, the liver is nourished; 
and thus, according to all analogy, it becomes entirely venous blood, on 
emerging from the capillaries of the liver into the radicles of the hepatic 
veins. This blood must, therefore, enter the right auricle from the inferior 
cava as venous blood ; and thus the pure placental blood, passing through 
the ductus venosus, has been mixed with five times* as much venous blood, 
at least, by the time it has arrived in the right auricle ; and the mixture is 
now but one-sixth placental, and five-sixths venous blood. This, also, will 
be the blood to enter the left auricle, provided no further admixture pre- 
viously obtains. 
But it is also assumed that the foetal liver, as well as the placenta, is a 
" depurating " organ ; and, therefore, the blood discharged by the hepatic 
veins is arterial (i. e., aerated) blood, as well as that transmitted by the 
ductus venosus. By a depurating organ must here obviously be meant an 
organ that renders impure or venous blood arterial; or that eliminates car- 
bonic acid .gas from it, and replaces the same by oxygen. No one, how- 
ever, it is believed, will distinctly assert that the liver has any such function 
as this. 
It is wrell known that in the adult, the liver is an eliminator of carbon 
from the blood, and is therefore, in this respect, a depurating organ. It is, 
however, such, only so far as it secretes bile ; and in doing this, it does not 
convert venous into arterial blood. We may, therefore, admit that in the 
foetus also, the liver separates carbon from the blood, so far as it secretes 
bile; while, at the same time, there is no reason to believe that it can pos- 
sibly in any degree convert venous into arterial blood ; or, much less, ren- 
der placental blood more highly arterialized. 
To what extent, therefore, the liver secretes bile in the foetus, is an 
important inquiry in this connection. In the adult, bile is secreted for two 
entirely distinct objects,-1st, to aid the process of digestion; and, 2d, to 
separate, at the same time, certain hydro-carbon compounds from the blood, 
as a depurating organ, in the sense last specified. These impurities are 
separated from venous blood; and such as, being collected by the vena 
portae from the alimentary canal and its appendages below the diaphragm, 
contains the crude elements of the food, abounding in the hydro-carbon 
compounds alluded to. 
* Twice as much in inferior vena cava ; as much from branches (7) of vena porta? 
and twice as much from two hepatic veins. 12 
On the other hand, in the foetus, the bile cannot be secreted in aid of 
digestion at all. Moreover, the blood from the alimentary canal does not 
here differ from venous blood in other parts of the foetus ; it being nowhere 
laden with the hydro-carbon compounds derived, in the adult, from the 
food. Very little bile, then, it may be supposed, is separated as an impurity 
from this venous blood in the formative branches of the vena portae, though 
a very small quantity may possibly be there separated. But there is no 
other source for bile besides, except the pure placental blood in the liver 
from the umbilical vein ; and to suppose this secretion to be separated from 
arterial blood, is both to adopt an idea opposed to all analogy, and, at the 
same time, to assume a necessity for the production of such a secretion from 
elements assumed to exist in the placental blood ; while there is not a shadow 
of reason for believing either in such a necessity, or in the existence of such 
elements. 
But we are still pointed to the fact, that the meconium found in the 
alimentary canal at birth contains nv>ne of the peculiar elements of bile ; 
and to this fact we are by no means indisposed to give its due weight. It 
has already been admitted that the foetal liver may secrete a small amount 
of bile from the venous blood derived from the formative branches of the 
vena portae ; and the following facts go to prove that the amount actually 
is very small. 1. The whole quantity of meconium secreted during foetal 
life (none being evacuated till after birth) is small; and yet more than the 
last half of foetal life* is required to produce the small amount found in the 
intestines at birth-a fact showing how slowly it is separated from the 
blood. But, 2d, only a comparatively small part of the meconium is 
actually bile. According to Dr. Davy's analysis,! 100 p?l»U of meconium 
consist of- 
Water, . . . . . 72.7 
Mucus and epithelium scales, . . 23.6 
Cholesterine and margarine, . . .0.7 
Coloring and sapid matter of bile and oleine, 3.0 
Here we find less than 3.7 per cent, of matter peculiar to bile, while at 
least 8 per cent, of such matters are found in the pure secretion. The 
inference, therefore, is, that less than one-half of the meconium is actually 
bile. Simon's analysis of dried meconium leads to a similar conclusion; 
it containing only 40 per cent, of matter peculiar to bile, while dried bile 
contains 80 per cent, of such matter. 
We cannot, therefore, regard the foetal liver otherwise than as a very feeble 
depurating organ, though it is such in the sense last explained. But I sub- 
* No meconium is found in the duodenum till the fourth month is completed, 
f Simon's Chemistry of Man, Vol. II. 13 
mit that the bile is secreted, not mainly to depurate the blood of the foetus, 
but to secure the discharge of the mucus and epithelium scales from the 
alimentary canal immediately after birth, and thus to prepare it for the 
reception of food. At all events, it is believed that the conversion of the 
placental blood into venous, in the capillaries of the liver, as before 
explained, would far more than compensate for all the depurating power 
the liver can possess as a secretor of bile; and, therefore, that the placental 
blood transmitted by the hepatic veins into the vena cava does not enter 
the latter vessel in a purer state than it entered the liver. 
Consequently, it does not leave the foetal liver " in the condition of 
arterial blood and to say that, after it enters the vena cava, it " loses this 
character in some degree by the time it arrives at the heart," has been 
shown to be altogether too feeble an expression to cover the facts-five- 
sixths of all the blood entering the right auricle from the vena cava inferior 
being venous.* 
Why, then, is the liver so enormously developed in the foetus, if not a 
powerful depurator of the blood, as a secretor of bile ? Because it has 
another entirely distinct and but recently discovered function to perform. 
But this question will be more appropriately answered in our remarks on 
the sixth proposition. 
Proposition 2d.-In regard to the non-admixture of the blood from the 
inferior vena cava (five-sixths venous), while in the right auricle, with that 
entering the same cavity from the superior vena cava, certain doubts have 
already been expressed. Of course, all belief in the complete non-admixture 
is based upon the supposed peculiar action of the Eustachian valve, which 
(it is said) carries it at once through the foramen ovale into the left auricle. 
It has been shown that Dr. Reid's experiments on this point are entirely 
inconclusive, and that, on anatomical grounds, it is as probable that this 
valve has a more important relation to the circulation through the inferior 
vena cava, than to that through the foramen ovale. But such as still insist 
on this non-admixture, are requested to explain how, by any possibility, the 
two auricles can contract from 140 to 150 times a minute (as in the foetus) 
without securing some admixture, through the foramen ovale, of the blood 
* This proposition is adopted, it will be remembered, on the calculation that the 
ductus venosus carries one-third of all the placental blood into the vena cava inferior. 
But if even one-half be assigned to this duct, and no allowance at all be made for the 
blood carried into the liver by the formative branches of the vena portae, it would 
still follow that three-fourths of all the blood poured into the right auricle from the 
inferior cava is venous blood. No one, it is believed, can demand such an assign- 
ment, however, with a knowledge of the facts I have stated, or will doubt that five- 
sixths is a more accurate calculation. 14 
distending the two auricles ? And if this result does occur at all, then the 
object of the supposed non-admixture of the two currents in the right auricle 
is just so far frustrated ; and it is hardly probable that a special mechanism 
is provided to keep the blood from mixing when it first arrives in the right 
auricle, and another which secures its admixture the t] oth part of a minute 
afterwards. Or, if it be remarked that the valve of the foramen ovale pre- 
vents the mixture of the blood through the foramen, we will recur to the 
period of foetal life, when there was no septum at all between the auricles, 
and the subsequent period when the foramen exists, but no valve is yet 
formed. Must there not be a complete admixture of all the blood in the 
auricles up to this time ? And must not this admixture through the fora- 
men continue, only diminishing in proportion as the valve of the foramen 
becomes more complete. 
. In a foetus of somewhat more than six months, I find the valve occludes 
near three-fourths of the foramen, and in one of eight and a half months, 
about five-sixths of it. It will, therefore, admit still of a considerable 
degree of mixing of blood through it; and not until the foramen is com- 
pletely closed (which, of course, never occurs till after birth), can all admix- 
ture through it be prevented. But this partial prevention of admixture is 
not the object of the development of the valve of the foramen, but merely 
incidental to its formation. Nor is the well-being of the foetus at all com- 
promised by such admixture, though the contrary has been hitherto 
affirmed. The following considerations will illustrate this point. 
It has already been stated, that at one period of foetal existence, the 
circulation is analogous to that of a fish. At this time the heart consists, 
as in the fish, of a single auricle, a single ventricle, and a bulbus arteriosus. 
Subsequently, the ventricle is divided into two cavities, by the formation of 
a septum, completed at the ninth week; and now the foetal heart is, in 
respect to its function, precisely that of the reptile, and consists of two ven- 
tricles and a single auricle.* This is, in fact, the type of the foetal circula- 
tion till birth. The septum between the two auricles, first appearing at 
about three months, is for some time very imperfect, from the opening 
called the foramen ovale remaining very large; then the valve of the 
foramen ovale gradually diminishes the opening, as it increases in size, and 
in the same proportion interferes with the mixture of the blood in the two 
auricles during their contraction. But we must regard the formation of the 
valve merely as a gradual approximation to the type of circulation to come 
at once after birth, and to the construction of the true mammal heart-of 
two auricles and two ventricles-which is required by that new mode of 
* The precise difference between the foetal and the reptile heart in structure, will 
appear on a subsequent page. 15 
existence. We can only say, the valve, by its gradual development before 
birth, has, by that time, produced a mammal heart, as nearly as is consist- 
ent with a reptile circulation; and which may at once act as a mammal 
heart when birth takes place. The foramen ovale is perfectly closed in 
about eight days after birth ; and then the true mammal heart becomes 
perfect, in structure as well as in function. 
But though the valve of the foramen ovale may, incidentally, to some 
extent prevent admixture of the blood in the two auricles, while they are 
contracting during the last few weeks of fcetal life ; still, this result is of no 
importance whatever, since it will now be shown that the blood in the left 
auricle is, on its first arrival in that cavity, probably quite as impure as that 
in the right auricle. 
This proposition implies that the Eustachian valve does not prevent an 
intermixture in the right auricle of the blood from the inferior vena cava 
with that from the superior cava, by directing the former current at once 
from the vein through the foramen ovale-as is assumed. Objections to 
Dr. Reid's experiments have already been made, and others will now be 
added. 
1st. If the Eustachian valve is formed to turn the current from the 
inferior vena cava at once through the foramen ovale, it must be admitted 
that its position is very unfavorable for the accomplishment of that object. 
The best position would evidently be secured, if it projected from the outer 
wall of the vein, and thus presented its free border towards the foramen 
ovale, in a line extending antero-posteriorly. According to my observa- 
tions, it actually projects from the anterior wall of the vein, though 
obliquely, so as to terminate at the antero-inferior border of the foramen 
ovale. Sometimes, however, it is attached even to the middle of the pos- 
terior (or left) border of the foramen ovale; a position far more unfavorable 
than the one just mentioned. A glance at the following figure will illus- 
trate this point. 
2d. It has been remarked, that if the Eustachian valve does keep the 
purer blood from the inferior vena cava from mixing with the less pure 
blood from the superior cava, we should expect it would remain perfect till 
birth ; while in fact it becomes atrophied from the seventh month, and 
continues to diminish, while the valve of the foramen ovale increases in 
size. 
3d. The increase of the latter valve, while the Eustachian is diminishing, 
might seem to imply that the former comes, in some degree, to supply the 
place of the latter. But it is impossible that the former can, in any degree, 
direct the blood from the inferior vena cava through the foramen ovale. 16 
Fig. III.-Modified from Weber. The 
Eustachian valve at six months. A-Inferior 
vena cava. B-Superior vena cava. C-Eus- 
tachian valve in front of termination of A; 
its inner extremity attached even to the mid- 
dle of the posterior border of the foramen 
ovale, D. The upper end of the probe pass- 
ing through the inferior vena cava, rests on 
the posterior wall of the right auricle ; and 
just below it is the opening of the coronary 
vein, partly closed by its valve. 
It is inferred, therefore, that the Eustachian valve is not formed to 
" prevent in great degree, if not entirely," the admixture of the blood from 
the inferior with that from the superior cava. That it may have some effect 
of this kind while the valve is largest, is possible; but this possible effect is 
incidental to another function, and in itself, if actual, is of no physiological 
importance whatever. 
What, then, is the true function of the Eustachian valve ? After much 
reflection, and study of its form and relations, the ideas of Winslow,* pub- 
lished nearly one hundred and fifty years ago, seem the most philosophical, 
viz., that it opposes the regurgitation of the blood from the right auricle 
into the inferior vena cava ; while it also, as Lancisi maintained, prevents 
the current from the superior cava from falling too forcibly upon that of the 
cava inferior. The effects of such a regurgitation in preventing the arrival 
of the placental blood in the heart, need not be specified; and it is equally 
apparent that if this be the true function of this valve, it is replaced, so far 
as regurgitation, from the left auricle, and then into the inferior cava is 
concerned, by the valve of the foramen ; and, therefore, in proportion as the 
latter is developed, the former may become atrophied, as already explained. 
It may, also, be added, that the position of the Eustachian valve, though 
unfavorable for directing the blood through the foramen ovale, is the only 
possible one in which it could both prevent regurgitation and break the 
impetus of the current from the superior vena cava, and, at the same time, 
not much obstruct the passage of the blood through the foramen ovale. 
These three results are, however, unimportant after birth, and when no pla- 
cental or arterial blood is to enter the right auricle ; and hence the valve 
is atrophied and useless after that event. 
» Memoires de 1'Academic Royale, 1717. 17 
3d Proposition.-Before entering upon this, we may recapitulate the 
two principal points just established, viz.: 
1. That of the blood arriving in the right auricle from the inferior vena 
cava, about one-sixth is pure placental blood, and five-sixths are venous; and, 
2. That the Eustachian valve has little, if any, power (and none, certainly, 
in the last part of foetal life) to prevent the admixture of the blood arriving- 
in the right auricle from the two vense cavfe. 
Now, admitting that the superior vena cava discharges but one-half as 
much blood as the inferior-and which is certainly a sufficiently low esti- 
mate-it will add three parts more of venous blood to the three of venous 
and one of placental blood from the inferior vena cava; and thus, of all the 
blood filling the right auricle, one-ninth will be placental and eight-ninths 
venous.* It has also been shown that the same mixed blood must enter 
the foramen ovale and fill the left auricle, except so far as the Eustachian 
valve may possibly, incidentally, and in less degree as the full term 
approaches, direct a somewhat larger proportion of the blood from the 
inferior cava through that opening, than of that from the superior cava. 
If, however, any difference as to the purity of the blood in the two auricles 
be produced in this way, it must be before the Eustachian valve is much 
atrophied ; and, therefore, at the time when, the valve of the foramen ovale 
being still slightly developed, the blood in the two auricles will be mingled 
through the foramen ovale at each contraction. We, therefore, conceive 
no essential difference as to the purity of the blood in the two auricles can 
exist. If, however, it be still asserted that the blood would not be mixed 
to any considerable extent through the foramen during the last four to six 
weeks before birth, let it be remembered, both that the Eustachian valve 
cannot then perform its assumed function, and also that the blood in the 
left auricle is constantly rendered less pure by the venous blood entering it 
directly from the lungs, through the pulmonary veins. The amount of 
venous blood thus returned is far greater than has been hitherto admitted, 
being about two-thirds of all sent through the pulmonary arteries. The 
improbability is therefore extreme, that the blood in the left auricle is' 
essentially, or indeed in any degree, purer than that of the right auricle. 
It may also be remarked that the dilatation or diastole of the auricles, 
exerting a suction power on the blood entering these cavities from the veins, 
would also commingle' the blood as it enters the right auricle, and then 
passes through the foramen ovale to the left; and even before the auricular 
contraction takes place. 
* If three-fourths instead of five-sixths be insisted on (note, p. 13), then the 
blood filling the right auricle would be one-sixth placental and five-sixths venous. 
In either case, its highly venous character is established. 18 
We, therefore, perceive that when the ventricles contract, after receiving 
the blood from the auricles, the left ventricle does not send " arterial " blood, 
before undergoing any admixture, into the ascending aorta, &c.; but it 
sends a mixed blood, probably eight-ninths venous (and certainly more than 
five-sixths venous) into that vessel. Neither does the right ventricle send 
more venous blood into the pulmonary artery and onwards; the latter 
blood being as pure as the former, or five-sixths to eight-ninths venous. 
The same is true of the reptile, though the heart of the latter consists 
of two auricles and but a single ventricle. One auricle receives the venous 
blood from the whole body, like the right auricle of the human adult; the 
other receives the aerated blood from the lungs. Both contracting simul- 
taneously, these two kinds of blood are forced into the single ventricle, and 
there mixed; and the latter sends this mixed blood through the aorta to 
the body generally, and also through another much smaller vessel-the 
pulmonary artery-to the lungs, for further aeration; equally pure blood 
being sent through both these vessels. 
The foetus has a single auricle (actually at the third month and later, 
and practically until birth), and two ventricles. Yet, precisely as in the 
reptile, the same mixed blood is poured into the aorta and the pulmonary 
artery ; it being mixed, in the reptile, in the single ventricle, and, in the 
foetus, in the (practically) single auricle, before it enters the double ventricle. 
Why, then, is not the auricle of the foetus double and the ventricle single, 
as in the reptile? A little reflection will show that the arrangement 
actually existing in the foetus, is the only simple one which is compatible 
with the requirements of the case, viz., a temporary reptile circulation to be 
instantly changed to a permanent mammal circulation. 
What has so long been taught, therefore, in regard to the ductus 
arteriosus carrying venous blood into the descending aorta for a particular 
reason, must at length fall to the ground. 
Proposition. It does not, therefore, follow that the " head and supe- 
' rior extremities are supplied with blood nearly as pure as that from the 
placenta f though it is true that these parts are developed in advance of 
the trunk and lower extremities. Nor is it the fact that the last mentioned 
parts are supplied with a less pure blood than the others. It has been 
shown that the pulmonary artery receives as pure blood as the aorta. This 
is necessitated, also, from the physiological fact that the pulmonary artery 
is the nutrient artery of the lungs ;* as the history of the development of 
* Dr. Heale has recently demonstrated the same proposition; and shown that the 
ronchial arteries only give the vasa vasorum to the pulmonary, and supply the 
leura, also, in part. See April ('54) No. of the Monthly, p. 302. 19 
these organs clearly indicates; though it would carry me too far from my 
present purpose to explain this point at length. It has also been shown 
that the blood entering the aorta from the left ventricle is as impure as that 
contained in the right side of the heart. If still farther proof is required, it 
may be remembered that in cases of cyanosis, or patency of the foramen 
ovale after birth, the livid color of the face, and all other parts of the sur- 
face, affords a visual demonstration of the assertion that the aorta circulates 
highly venous blood. And can we suppose the blood in the aorta is purer 
before birth than afterwards ? 
It has been assumed that the earlier development of the head and supe- 
rior extremities, is at the same time an effect of their being nourished by a 
purer blood, and also a proof of such superior purity-a good illustration 
of what logicians term " reasoning in a circle." It has been shown that no 
such difference in the purity of the blood can exist. But this question will 
also be briefly considered, on independent grounds, since so much impor- 
tance has been attached to this assumption. 
It is true that the organs of sensation, deglutition, and prehension, are 
early needed and early developed; and this implies an early development 
of the brain and spinal cord-and, in a word, of the head and superior 
extremities. These parts are also supplied with blood from the arch of the 
aorta. But, it is equally true, that the alimentary canal, and the urinary 
apparatus, are quite as far developed at birth ; though the latter organs are 
all supplied by the descending aorta. A difference in tire purity of the 
nutrient blood cannot, therefore, account for the more early development. 
Or, if it still be insisted that wre may thus account for the facts, how then 
shall blood of equal purity, sent to the upper and lower extremities after 
birth, enable the latter to gain upon and overtake the advanced develop- 
ment of the former ? 
And, again, if a purer nutrient blood produces a more rapid development 
of the head and superior extremities of the human foetus, the same should 
obtain in all the mammalia-the foetal circulation being in all essentially 
the same; and we may inquire, why the posterior extremities of the calf, 
the sheep, and the dog, are, at birth, equally developed with the anterior 
extremities and the head ? 
Thus comparative physiology again leads us to the conclusion that there 
is no difference as to the purity of the blood contained in the ascending and 
the descending aorta, as it previously has indicated that the blood in the 
pulmonary artery and the ascending aorta are, in respect to purity, the same. 
How, then, shall we account for the earlier development of the head and 
superior extremities ? We can only say it is an ultimate fact-a law of 
development. And yet, it is certainly no more difficult to explain how they 
are first developed while they receive the same blood as the lower extremi- 20 
ties, than it would be to explain why the alimentary canal and kidneys are 
equally developed with them, on the other supposition-that the latter are 
nourished by an inferior blood. 
The great law of development appears to be, that " the parts and organs 
first needed are first developedand is applicable also to different parts of 
the same apparatus, and even to different portions of the same organ, e. g., 
the ribs are developed earlier than the sternum-the bones at the base of 
the cranium earlier than those of the vertex-the laminae of the vertebrae 
before the bodies, and those of the dorsal region first of all-and the organ 
of sight previously to that of smell. But, as the parts and organs needed, 
immediately after birth, vary in different animals, we find a corresponding 
difference in development up to that period. The young of the marsupialia, 
remaining, for some time after birth, in a pouch, and attached to the mam- 
milla of the mother, is an embryo, rather than a foetus, when born, so far 
as development is concerned. The herbivora and carnivora, needing 
immediately to be able to stand and walk, have all the four extremities 
equally developed at birth. The human infant is very differently circum- 
stanced in this latter respect; and to distend the uterus during gestation 
with a pair of well-developed inferior extremities, which are not to become 
available for several months after birth, would certainly be productive of 
some inconvenience, without any compensating advantage ; especially since, 
as things now are even, the motor powers of these less-developed limbs are 
not seldom by mothers found to be inconveniently energetic. 
Thus, the idea of a purer blood being sent to the head and upper extremi- 
ties, is shown to be untenable, from whatever point of view we consider it. 
And, as it was suggested at first, from a mere desire to account, and for the 
special purpose of accounting, for the earlier development of the upper parts 
of the foetus-and other facts have been perverted to support it-it is, at 
last, high time to remand it back to the brain, now long since mouldering 
in dust, which first conceived it. 
5 th Proposition.-We have next to show the incorrectness of the asser- 
1 tion, that "in the foetus the lungs are solid and almost impervious and 
that the 11 greater part" of the blood in the pulmonary artery "rushes 
through the ductus arteriosus " into the descending aorta. 
It is true that the foetal lungs are more solid than they are after birth, 
but no more so than the liver or the kidneys; and therefore we discover no 
reason why they are more impervious to the circulation than these organs- 
which transmit an abundance of blood. Moreover, we have discovered a 
reason for admitting a free circulation through the foetal lungs, in the com- 
paratively Large size of the pulmonary arteries and veins; and a necessity 
for such a circulation, since the pulmonary arteries are the nutrient arteries 21 
of the lungs. It has been seen that, if we may judge from the size of the 
two branches of the pulmonary artery, compared with that of the ductus 
arteriosus, about two-thirds of all the blood sent from the right ventricle 
traverses the lungs; and is, of course, returned as venous blood to the left 
auricle, by the pulmonary veins. In the foetus, a mixed blood is sent through 
the lungs for their nutrition, for entirely venous blood will not accomplish 
that object; in the adult, venous blood is sent through the lungs first for 
" oxydation," or aeration; and secondly, for the nutrition of the lungs after 
aeration is secured.* 
Thus, also, the " greater part " of the blood in the trunk of the pulmo- 
nary artery does not rush through the ductus arteriosus-only about one- 
third of that blood is transmitted through this duct. It has also been shown 
that the blood it transmits is as pure as that sent from the left auricle 
directly into the ascending aorta. The ductus does not, therefore, terminate 
in the descending aorta, in order to avoid mixing its impure blood with 
that sent to the head and upper extremities, but for some other reason; and 
we deem it unnecessary to look for it beyond the fact that the commence- 
ment of the descending aorta is the nearest point in that vessel which the 
ductus can enter. What, then, is the true function of the ductus arteriosus ? 
It is, we conceive, merely a " waste pipe," to conduct at once into the aorta 
all that part of the blood in the trunk of the pulmonary artery which the 
collapsed foetal lungs cannot receive. Hence, as soon as the lungs are dis- 
tended by the first inspiration, and thus made capable of receiving and trans- 
mitting all the blood sent from the right auricle and ventricle into the trunk 
of the pulmonary artery, the ductus becomes at once useless, and, together 
with the foramen ovale and the ductus venosus, becomes completely closed 
about eight days after birth.f 
But while the fact is insisted on, that the pulmonary artery and the 
aorta carry equally pure blood, it must be remembered that in both these 
vessels there is not more than one part of pure placental blood to six or 
eight of venous blood. Thus the blood in the arteries of the foetus is but 
slightly more pure than the venous blood of the adult. It seems to have 
been taken for granted that the organs of the foetus (the head and upper 
extremities, at least) must be developed from pure arterial blood-blood as 
pure as the arterial blood of the adult. It is now apparent that no such 
blood exists in any artery possessed by the foetus; but only in the umbilical 
* For an explanation of this, see the Monthly, April No., 1854, p. 303. 
f Billard found that of nineteen infants who had lived but one day, the foramen 
ovale was completely open in fourteen; in two, it had begun to close; and in two it 
was completely shut. Of twenty who had died on the eighth day, five only still had 
the foramen open.-Traite des Maladies des Enfans nouveau-nes, 1828. 22 
vein, and the ductus venosus. All the organs of the reptile are also devel- 
oped from a mixed blood. 
But while blood of equal purity is sent through the pulmonary artery and 
the aorta in the human foetus, the blood returned to the placenta for farther 
purification is just as pure also. The umbilical arteries are merely continua- 
tions of the internal iliac arteries, and, of course, contain the same blood as the 
aorta. But here, again, the analogy to the reptile is perfect; the mixed blood 
in the single ventricle being sent, in part, through the pulmonary artery 
and lungs for farther aeration, while the rest is sent through the aorta and 
its branches, for the nutrition of the body generally. In the reptile, more- 
over, the pulmonary artery is smaller than the aorta, and less blood passes 
through the lungs than through the aorta and to the tissues generally. In 
the foetus, also, much more blood passes through the aorta than to the pla- 
centa-it having been shown that the umbilical arteries cannot transmit 
more than one-sixth of all the blood received by the aorta at its commence- 
ment. In the human adult, as much blood is sent through the lungs as 
through the aorta and its divisions; and it is calculated that the whole 
mass in the body may pass through them, and therefore become aerated in 
the space of three minutes; the standard of aeration in the adult is there- 
fore high. In the foetus, on the other hand, the umbilical arteries can return 
the blood to the placenta only about one-sixth as rapidly in proportion as 
it is circulated through the lungs in the adult; and, therefore, the standard 
of aeration in the fcetus, as in the reptile, is low. And the mixed blood in 
the umbilical arteries being returned as pure placental blood by the umbili- 
cal vein, this low standard of aeration of the mass of blood in the arterial 
system of the foetus is thus constantly maintained, though the quantity of 
pure blood returned to the heart through, the ductus venosus is so small. 
There are other peculiarities of arterial foetal blood, besides its venous 
character and appearance, as (compared with the mother's blood) its abun- 
dance of colored corpuscles, and its deficiency of fibrine. But, upon these pecu- 
liarities I need not dwell; nor is farther proof required, it is believed, of the 
incorrectness of the proposition now under consideration. And should it, at 
any time, be proved that even one-half of the blood in the trunk of the pul- 
monary artery traverses the ductus arteriosus, its physiological inaccuracy 
would remain unchanged. 
6th Proposition.-There can be no doubt that the large size of the foetal 
liver is the direct result of the distribution to it of a large amount of the 
pure placental blood. Indeed, it has been shown that while all other organs 
in the foetus are nourished from a mixed blood (not more than one-sixth 
placental) this organ alone is nourished by a mixture of three-fourths pla- 
cental blood. A comparatively early and enormous development might 
reasonably be expected, therefore; and it is found actually to obtain. 23 
But we cannot regard this enormous development as merely a casual 
result of the distribution of a great amount of pure blood to the foetal liver, 
as the quotation constituting the proposition now under consideration seems 
to imply. We believe the law of development, before mentioned, is as 
applicable here as. elsewhere ; and that the blood is sent to the liver on pur- 
pose to develop it-it being largely and early developed, because early 
needed, in the foetal economy. 
What, then, is the function of the foetal liver requiring so early and so 
enormous a development ? The liver of the reptile is also largely devel- 
oped, and here we discover another analogy with the human foetus. We 
have also seen, that it cannot be as a secreter of bile that the liver is so early 
needed. Bile is not found in the intestine at all till the fifth month; and 
it has been shown that only a small quantity, in the aggregate, can have 
been secreted previously to birth. On the other hand, the liver is one of the 
first organs becoming distinct in the embryo, constituting, from three to five 
weeks, over one half the weight of the entire embryo; almost entirely filling 
the abdomen at twelve weeks; and constituting T'g part of the weight of the 
whole body at birth. The inference is, therefore, that the liver performs 
some function before it becomes a secreter of bile, to a perceptible extent- 
that this is a more important function than the one later manifested-and that 
it continues in full activity till birth, when it diminishes. 
Those who are familiar with the recent experiments of Bernard, of Paris, 
will not hesitate to decide, that the function of the liver, as a blood-making 
organ, is the one in question. For, it must not be forgotten, that the foetus 
makes its own blood; not deriving a particle of blood from the mother's 
vessels-but merely the elemen ts from which it forms its own vital fluid. That 
the liver is the organ most important in the blood-making process, has been 
demonstrated by Bernard ; and, surely, there is no time when its action is 
so much required as when the first blood is to be formed, and increased, 
and all the tissues are to be developed-from elements obtained from the blood 
of the mother. Hence the large development of this organ in the foetus. 
But the liver actually diminishes in size at once after birth-the dimi- 
nution affecting principally the left lobe; and which, in the foetus, is about 
as large as the right. Indeed, it is not till the infant is from ten to twelve 
months old, that the liver has again become as large as it was at birth. 
Doubtless the withdrawal of the pure placental blood from this organ at 
birth, and the substitution of mere venous blood in the vena portae, is the 
immediate cause of this atrophied condition of the organ for a time. Still 
we cannot regard this condition as merely accidentally owing to that cause. 
The blood of the new-born infant is to be formed from elements contained in 
food, and not derived, as before, directly from the mother's blood-current. 
True, the milk naturally destined for its nourishment, is also obtained from 24 
the mother's blood. But the gland secreting it has elaborated its elements 
from the blood; and, it being digested before entering the liver, Jess of 
the peculiar action of the latter organ is probably required in the blood- 
making process. When, however, the child begins to take a variety of 
aliment-or when somewhat more than a year old-the liver is found to 
have regained its weight at birth, and now gradually proceeds to its full 
development in the adult, when it constitutes about part of the entire 
weight of the body. These remarks are, however, made, not so much to 
explain the atrophy of the liver after birth, but as naturally suggested by 
and associated with its occurrence. 
The vena portae in the foetal liver is, therefore, in all respects, an artery ; 
it carries the pure blood from the placenta, and is the nutrient artery of the 
liver, as the pulmonary is of the lungs. It is, however, also, something 
more. The formative branches constitute the true vena portae in the foetus, 
as well as in the ; and, therefore, its branches in the substance of the 
liver, containing the venous blood from these-mixed with the placental 
blood, as before explained-represent the vena portae in the liver of the 
adult, containing only venous blood, from which the bile is secreted-at the 
same time that it is also the nutrient artery of this organ. After birth, the 
hepatic artery, which, in the foetus, does hardly more than afford the vasa 
vasorum to the vena portae, becomes the sole nutrient artery of this organ, 
as it alone transmits arterial blood. For the assumption appears well 
founded, that after birth the tissues can be developed and repaired from 
arterial, or completely aerated, blood alone; while the tissues of the foetus 
are formed, as has been proved, from a mixed blood, of which (except, in 
case of the liver alone) the venous forms from five to eight times as large 
a proportion as the placental or aerated blood. 
Having completed my examination of the propositions under consider- 
ation, I now conclude with a recapitulation of the conclusions which have 
been arrived at, and which together constitute, it is believed, such a view 
of the foetal circulation, during the last half of foetal life, as the present state 
of physiological science demands. 
The view of the foetal circulation required by the present state of physiolog- 
ical science. 
1st. The human foetus, during the last half of foetal existence, has a rep- 
tile circulation-the mammal circulation commencing at birth; and the 
structure and the function of each particular part of its circulatory appar- 
atus are in subservience to this fundamental fact. The characteristics of 
reptile circulation are-1, the circulation of a mixed blood (and of the same 
degree of impurity) through both the aorta to the tissues, and through the 25 
pulmonary artery to the lungs ; and 2, the transmission of far less blood to 
the aerating apparatus than is sent through the aorta. 
2. The foramen ovale with its valve is the only simple mechanism which 
could answer the requirements of the case, viz., a temporary reptile circu- 
lation with a capability of instantaneous change to a permanent mammal 
circulation, the foramen becoming permanently closed about eight days after 
birth. 
3. The ductus arteriosus is merely a " waste pipe," conducting into the 
nearest portion of the aorta that part of the blood sent into the trunk of the 
pulmonary artery, which the collapsed lungs of the foetus are unable to re- 
ceive. After birth the latter admit all the blood, and the ductus is, there- 
fore, useless. It does not enter the descending aorta to avoid sending its 
blood to the head and upper extremities. 
4. Though the lungs are more solid in the foetus than after birth, they 
are probably permeated by about two-thirds of the blood entering the trunk 
of the pulmonary artery, and this is returned as venous blood to the left 
auricle. 
5. The blood arriving in the right auricle from the two venae cavse is 
completely intermixed by the diastole and systole of this cavity; and the 
same mixed blood is therefore transmitted through the foramen ovale into 
the left auricle. Or, if by any possibility more placental blood enters that 
cavity, the venous blood returned by the pulmonary veins most probably 
counterbalances that advantage. 
6. The Eustachian valve cannot prevent the admixture of the blood from 
the venae cavae, nor direct that from the inferior cava at once through the 
foramen ovale; it merely prevents regurgitation from the auricle into the 
inferior vena cava, at the same time incidentally preventing the current from 
the superior cava from impinging so forcibly upon that of the inferior. 
Hence the valve of the foramen ovale replaces it to some extent, in respect 
to its principal function ; and, therefore, it becomes atrophied in proportion 
as the latter is developed. 
7. No artery in the body of the foetus contains arterial blood. The 
aorta and pulmonary artery, and all their branches, contain a mixed blood, 
about five parts, at least, venous to one part placental. The precise pro- 
portions, however, are unimportant, the blood being of a highly venous 
character, and as impure in the aorta as in the pulmonary artery. Only the 
umbilical vein and the ductus venosus contain pure aerated placental blood. 
8. The umbilical arteries contain the same mixed blood as the aorta, and 
possibly return one-sixth of the blood received by that vessel; but this 
amount, aerated in the placenta and returned by the umbilical veins, suffices 
to maintain the low standard of aeration in the foetus. 
9. The head and upper extremities of the foetus do not receive a purer 26 
blood than the lower parts of the body. They, as well as the digestive and 
urinary apparatus, are earlier developed, in accordance with a general law 
of development. 
10. The foetal liver is a depurating organ only so far as it secretes bile, 
and therefore, to a slight extent, though it does not thus convert venous 
into arterial blood. Its large development, from the placental blood 
abundantly distributed to it, has relation to its function as a blood-making 
and not as a bile-secreting organ ; and this blood becomes venous in the 
capillaries and the hepatic veins, as all analogy proves. 
11. The trunk of the vena portse is, in the foetus, both the nutrient 
artery of the liver, and also corresponds to the vena portse of the adult- 
its formative branches containing venous blood from which the bile in the 
meconium is probably secreted. 
12. Anatomy, the history of development, and comparative physiology, 
combine to sustain the preceding propositions. ■ 
Bowdoin College, April 1,1854.