explanation of digestive leucocytosis than that advanced by Pohl.
All animal foods, especially meat of various kinds and milk, contain
considerable nuclein or nucleo-albumins, which, by the action of the
gastric juice, are liberated and partially digested, but the nuclein
is certainly not dissolved. Nucleins, however, are soluble in weak
alkaline fluids, and when exposed to the action of the alkaline
pancreatic juice in the intestine, are in great part dissolved. Thus,
Popoff[226] has reported that different varieties of nuclein behave
somewhat differently in the intestine, according to their origin. In
young and tender tissues, solution of the contained nuclein through the
alkaline fluids of the intestinal canal is fairly complete, while the
older products are somewhat more resistant both to the pancreatic juice
and to the putrefactive processes common to the intestine. However,
experiments show that the greater portion of the nuclein of ordinary
proteid foods is dissolved in the intestine, and absorbed as such in
a practically unaltered form. Consequently, passing into the adenoid
tissue surrounding the intestine, it has a marked stimulating action
on the lymphoid elements, accompanied by a noticeable increase in the
number of leucocytes, which are perhaps produced at the expense of a
portion of the proteoses and peptones formed during proteolysis.
[226] Ueber die Einwirkung von Eiweissverdauenden Fermenten auf die
Nucleinstoffe, Zeitschr. f. physiol. Chem., Band 18, p. 533.
Thus, my interpretation of these results would lead me simply to the
admission that, possibly, a portion of the products of proteolysis
might pass from the intestine into the blood-current indirectly,
through the bodies of the leucocytes formed in the adenoid tissue
of the intestine. But even admitting this, we lack positive proof
of any direct transformation of proteoses and peptones into the
organized material of the white blood-corpuscles, for it may be that
the above products are first transformed through other agencies into
serum-albumin, or other like proteids. There are, indeed, many facts
which are plainly opposed to any marked absorption and transformation
of peptones by the leucocytes of the intestinal mucous membrane. Thus,
Heidenhain[227] has severely criticised the theory on the ground that
there is very little increase in the flow of lymph from the thoracic
duct during absorption, and further that the small percentage of
proteid matter in the chyle (about 2.0 per cent.) cannot account for
the large amount of proteid absorbed. Further, the objection is made
that the leucocytes present in the intestinal mucosa, though numerous,
are wholly inadequate to assimilate any large proportion of the
ingested proteid food.
[227] Beiträge zur Histologie und Physiologie des Dünndarms, Pflüger’s
Archiv f. Physiol, Band 43, Supplement Heft.
Still greater stress, however, may be laid upon the fact that
experimental evidence points to the conclusion that lymph-cells
cannot assimilate either peptones or proteoses. Thus, quite recently,
Shore[228] has studied the results following the introduction of a
mixture of such products into the lymphatic system by secretion,
by absorption, and by direct injection into a lymphatic vessel.
Preliminary experiments on dogs showed that when peptone is introduced
into the bile-duct it gradually appears in the lymph of the thoracic
duct, consequently this method can be made use of as a means of
ascertaining the fate of peptone so absorbed into the lymphatic system.
The results obtained, using the ammonium sulphate method for the
isolation of the peptone, showed that when peptone is injected into
the bile-duct with sufficient force to overcome the low pressure under
which bile is secreted, there is an increase in the rate of flow of
lymph from the thoracic duct. Further, while peptone is somewhat slow
in appearing in the lymph it eventually makes its appearance there, in
from sixty to one hundred and forty minutes after its injection into
the bile-duct. A certain amount of peptone naturally passes into the
blood, but is then rapidly excreted through the urine. When, however,
the renal vessels are ligatured, peptone still rapidly disappears from
the blood, but then passes into the lymph, and under such circumstances
can be detected in the lymph as early as thirty-eight minutes after its
injection into the bile-duct. These results, therefore, do not accord
with the view that peptones suffer marked transformation by contact
with lymph-cells, for when only three-fourths of a gramme of peptone
is introduced into the bile-duct, unaltered peptone can be detected
in the lymph of the thoracic duct seventy to ninety minutes after its
injection.
[228] On the Fate of Peptone in the Lymphatic System, Journal of
Physiol., vol. xi., p. 528.
With reference to the fate of peptone when it passes by secretion into
the lymphatic system, it will be remembered that Heidenhain[229] has
shown that the injection of peptone into the blood may be followed by
a large increase in the rate of flow of lymph. Further, the amount of
solids in the lymph, especially of proteids, is considerably increased.
From these and other facts, Heidenhain is led to the view that the
formation of lymph is a true secretion from the blood-vessels. Shore
finds that when small amounts of peptone are slowly injected into the
blood, there is generally only a slight acceleration in the flow of
lymph, but the clotting power of the lymph is affected in a remarkable
manner. Thus, about twenty minutes after the commencement of the
injection the lymph loses entirely its power of coagulating. This
continues for about twenty minutes, and then, in spite of the fact that
the injection is being continued, the lymph rapidly regains its power
of clotting, and finally coagulates quicker and firmer than before.
This peculiar action of peptone on the clotting power of lymph may
frequently be observed, even when the amount of peptone present is too
small to be detected with certainty by chemical methods. Thus, when
peptone in small quantity is injected very slowly into the blood, the
greater part of it escapes through the urine, but a small fraction,
sometimes too small to actually detect, passes into the lymph and shows
its presence by its peculiar influence on the clotting of the fluid.
[229] Versuche und Fragen zur Lehre von der Lymphbildung, Pflüger’s
Archiv f. Physiol., Band 49, p. 252.
When, on the other hand, peptone is injected rapidly into the blood,
0.3 to 0.6 gramme per kilo. during two to ten minutes, it may disappear
completely from the blood in five to ten minutes after the end of the
injection. In such a case, the fall of blood-pressure induced leads to
more or less arrest of the renal secretion, peptone appearing in large
amount in the lymph; but there is no indication of any alteration of
the peptone by the lymph, or its contained leucocytes. Thus, when there
is no chance for the peptone to escape from the body, as on ligation
of the renal vessels, the peptone injected into the blood is rapidly
thrown into the lymph, and from the lymph in the tissues of the body it
is gradually carried to the thoracic duct, and then again passes into
the blood; all of which shows that there is little or no transformation
of the peptone by the leucocytes of the lymphatic system.
Further, by direct injection of peptone into a lymphatic vessel,
Shore has shown that even so small an amount as 0.049 gramme is not
assimilated or transformed by the lymph in half an hour. Consequently,
we seem to have strong evidence that peptones are not prone to direct
alteration of any kind by the leucocytes of the lymphatic system.
Further, it would appear that the lymphoid cells of the spleen are
equally unable to assimilate small amounts of peptone injected into
the splenic artery. Leucocytes, then, can play no direct part in the
absorption of the products of proteolysis from the intestine; the lymph
is normally free from both proteoses and peptones, and the leucocytes
plainly have no power to transform these bodies into other forms. They
can only utilize the proteid material elaborated from the products of
proteolysis by other agencies.
Plainly, proteoses and peptones in the blood and lymph are foreign
substances. When present in the circulation they give rise, as we
have seen, to an increased flow of lymph and to a change in the
coagulability of the blood. Further, not only is the flow of lymph
augmented but there is likewise an increase in the amount of solid
matter, while a corresponding decrease is noticed in the solid matter
of the blood-plasma. This fact obviously gives support to the view
that the increased formation of lymph after the injection of peptone
is due to an active process of secretion by the endothelium cells of
the capillary walls.[230] Further, as we have seen, peptone disappears
from the blood more or less rapidly after its injection, so that it
is quite possible that the loss or alteration of the coagulability
of the blood may not be due to the peptone itself, but rather to an
altered condition of the blood induced by the peptone. Moreover, this
altered condition of the blood may be the real cause of the increased
transudation, or secretion of lymph so conspicuous after the injection
of peptone. Starling, however, by carefully conducted experiments
on dogs finds, in conformity with Heidenhain’s views, that peptone
injected into the blood exercises a direct excitatory effect on the
endothelial cells, causing thereby an increased flow of lymph; the
increased flow being in no way caused by the change in the blood that
is simultaneously produced. Further, it would appear, according to
Starling’s views, that the change in the coagulability of the blood is
not due to the effect of the peptone on the endothelial cells of the
blood-vessels, or at least on their lymph-producing functions. Thus,
the injection of peptone may result in an action on the endothelial
cells of the blood-vessels, thereby increasing the flow of lymph, or
on the blood itself with a destruction or diminution of the clotting
power of the blood; the two results being more or less independent.
Further, the rapid transferences of peptone from the blood to the
lymph is effected by the selective activity of the endothelial cells
of the vessel-wall, and according to Starling it is probable that a
preponderating part is played by the endothelial cells of the renal
capillaries.
[230] Starling: Contributions to the Physiology of Lymph Secretion,
Journal of Physiol., vol. xiv, p. 131.
In view of all these statements, it is very evident that proteoses and
peptones once outside the limits of the alimentary tract may be passed
about from organ to organ and from secretion to secretion, inducing
changes here and there in their course, but suffering very little
change themselves. The main efforts of the system are directed to the
removal of these unwelcome strangers as speedily as possible, for their
marked physiological action renders them somewhat dangerous visitors.
As normal products of digestive proteolysis, they are never found
beyond the limits of the gastro-intestinal canal, but undergo
retrogression in their passage through the epithelial cells of
the intestinal wall, being presumably converted thereby into
serum-albumin,[231] which can be directly utilized for the nutrition of
the body; a conversion which is plainly dependent upon certain inherent
qualities of the living epithelial cells, and is doubtless of the
nature of a dehydration.
[231] See Kronecker and Popoff: Ueber die Bildung von Serumalbumin im
Darmkanale, Du Bois-Reymond’s Archiv f. Physiol., 1887, p. 345. Also
Nadine Popoff, Zeitschr. f. Biol., Band 25, p. 427.
End of Project Gutenberg's On Digestive Proteolysis, by R. H. Chittenden