Chapter III: ALBUMINOIDS.--A. Soluble in boiling water with formation of (4)

Further, as already stated, absorption of proteid food-stuffs, or their products, from the alimentary tract, is, under ordinary circumstances at least, limited to the intestine; from the stomach there is comparatively little absorbed, and if necessary we might advance this fact as an important argument against the theory of general absorption of proteids in the form of acid-albumin. Even such indifferent fluids as water, or physiological salt solution, are absorbed with extreme slowness from the stomach;[206] this organ showing very little ability to take up water even when the blood-vessels are dilated, as after the ingestion of food.

[206] J. S. Edkins: The Absorption of Water in the Alimentary Canal. Journal of Physiol., vol. 13, p. 445.

This brings us to a very important point in connection with the utilization by the system of the ordinary products of proteolysis. The latter, as we have seen, are mainly proteoses and peptones, and yet all the evidence points clearly to the fact that these substances are never present, at least in any quantity, in the blood or lymph, even when digestive proteolysis is at its height. Further, the very nature of the proteoses and peptones, their marked physiological action when they are introduced directly into the circulating blood, their rapid excretion, either as proteoses or peptones, by the kidneys when so introduced,[207] all indicate that they are foreign substances, totally out of their natural environment when introduced into the blood-current. And yet we very well know that proteoses especially are possessed of high nutritive qualities; they are abundantly able to support animal life. Thus, Politzer[208] found by feeding experiments with heteroalbumose, dysalbumose, and protoalbumose, that these bodies taken into the stomach have the same nutritive value as meat. Various feeding experiments with proteoses from different sources, carried out in my laboratory on young dogs, have shown conclusively that for short periods of time, at least, these hydrolytic cleavage products are fully as capable of sustaining the nitrogenous equilibrium of the body as the proteids from which they are derived. In fact, the results obtained favor the view that the proteoses, weight for weight, possess a higher nutritive value than fresh beef.[209] It may be questionable, however, whether such a result would follow in experiments conducted over longer periods of time, but of this we may be certain, that the proteoses formed in the alimentary tract can be absorbed and utilized by the system without their exerting any toxic action whatever.

[207] Franz Hofmeister: Ueber das Schicksal des Peptons im Blute, Zeitschr. f. physiol. Chem., Band 5, p. 125.

[208] Ueber den Nährwerth einiger Verdauungsproducte des Eiweisses, Pflüger’s Archiv f. Physiol., Band 37, p. 301.

[209] Compare Hildebrandt, Zur Frage nach dem Nährwerth der Albumosen, Zeitschr. f. physiol. Chem., Band 18, p. 120.

Consequently, we are forced to the conclusion that these primary products of proteolysis, so important in the nutrition of the animal body, must undergo some change during the process of absorption, by which they are converted into new bodies, less toxic in their nature, and better adapted for the direct nutritional needs of the organism. The same statement applies likewise to peptones.

The fact that peptones are not discoverable in the blood and lymph, even during or after active digestion, was practically ascertained years ago by such well-known workers as Maly, Adamkiewicz, and others. The natural supposition following this observation was that the products of proteolysis underwent some change in the hepatic cells; but this view was soon shown to be untenable by examination of the portal blood, which was found to be as free from peptone as the blood of the hepatic vein. Neumeister,[210] using the more modern methods of work and with the wider knowledge gained during these latter years, has shown conclusively that proteoses and peptones are never present in the blood, even when these substances are contained in the intestine in fairly large amounts. I can corroborate these statements from the results of my own experiments in this direction. Thus, I have taken a dog in full digestion, fed with an abundance of meat, and collecting the blood from the carotid artery have made a careful examination for peptone, by the following method: The blood was allowed to flow directly into a dilute solution of ammonium sulphate, sufficiently strong to prevent coagulation, and then shaken with ether to rupture the red blood-corpuscles. The solution, freed from ether, was next saturated with crystals of ammonium sulphate, by which the proteid matter was completely precipitated. The clear filtrate was then concentrated somewhat, the excess of the ammonium salt removed by filtration, and the filtrate carefully tested for peptone by addition of a large volume of a saturated solution of potassium hydroxide and a few drops of a dilute solution of cupric sulphate. The test was wholly negative, although the intestine of the animal showed the presence of both peptone and proteoses. This result, as I have said, is simply confirmatory of work done by others in this direction, notably Neumeister, and illustrates the statement that peptones are not to be found in the circulating blood, even after a full proteid diet. In this connection it is to be remembered that we have abundant proof of the rapid disappearance of both proteoses and peptones[211] from the intestine, either by absorption or otherwise. They certainly disappear, and, as we have seen, are not to be found in the blood. Further, Neumeister has confirmed the original observation of Schmidt-Mulheim,[212] that both chyle and lymph are practically free from proteoses and peptone, thus again forcing us to the conclusion that the primary products of proteolysis must undergo change prior to their passage into the blood or lymph.

[210] Ueber die Einführhrung der Albumosen und Peptone in den Organismus, Zeitschr. f. Biol., Band 24, p. 277.

[211] Rohmann: Ueber Secretion und Resorption im Dünndarm, Pflüger’s Archiv f. Physiol., Band 41, p. 440.

[212] Du Bois-Reymond’s Archiv f. Physiol., p. 33, 1880.

Many observations lend favor to the view that a transformation of some kind takes place in the intestine itself, not indeed in the lumen of the tube, but somewhere in the walls, through which the peptones must pass before reaching the blood. Thus, peptones placed in contact with pieces of the isolated, though still living, intestine, after a time completely disappear from view,[213] so completely that no reaction can be obtained even by the most delicate of tests. In support of this statement I may cite the results of several of my own experiments which certainly furnish evidence that true peptones undergo profound alteration by simple contact with the living mucous membrane of the small intestine. The method employed was similar to that made use of some years ago in a study of the influence of peptone on the post-mortem formation of sugar in the liver.[214] A large, well-nourished rabbit was killed by severing the carotid artery and the blood collected and defibrinated. Of this, 50 c. c. were mixed with an equal volume of 0.5 per cent. salt solution containing 1.25 grammes of pure amphopeptone, prepared from egg-albumin, the mixture obviously containing 1.25 per cent. of peptone. The fluid was transferred to a large, roomy flask, provided with a stopper having two holes, in one of which was fitted a long glass tube reaching below the fluid. The flask, with its contents, was then placed in a suitable water-bath at a temperature of 40° C.

[213] Salvioli: Eine neue Methode für die Untersuchung der Functionen des Dünndarms, Du Bois-Reymond’s Archiv f. Physiol., 1880. Supplement Band, p. 112. Neumeister: Zur Physiologie der Eiweissresorption und zur Lehre von den Peptonen, Zeitschr. f. Biol., Band 27, p. 324.

[214] Chittenden and Lambert: Studies in Physiol. Chem., Yale Univer., vol. i., p. 171.

The small intestine of the rabbit was carefully separated from the mesentery and from the pancreatic gland, and the upper portion cut open and quickly washed free from any contained matter or adherent secretions, by repeated immersion in 0.5 per cent. salt solution warmed at 40° C. This was repeated until the tissue was quite free from all impurities, after which it was cut into small pieces and immersed for a moment in a 0.5 per cent. solution of sodium chloride containing 1.25 per cent. of peptone. The tissue was then carefully collected on coarse muslin, allowed to drain, and then quickly transferred to the flask containing the warm blood and peptone. This mixture was kept at 40° C. for two hours, a slow current of air being bubbled through the fluid during the entire period. At the expiration of this time the fluid was separated from the pieces of tissue by nitration through muslin, and then saturated with ammonium sulphate after the usual method for the separation of albumoses, etc. On now testing a portion of the clear filtrate for peptone by the biuret test, not a trace of a reaction could be obtained. The entire amount of proteid matter present was precipitated by the ammonium salt, thus showing that the peptone originally added had been completely transformed into something precipitable by saturation of the fluid with ammonium sulphate. That this transformation of the peptone was accomplished mainly through the action of the intestine, was shown by a parallel experiment, in which all of the above conditions were duplicated, omitting only the pieces of intestine. Here, however, on testing the filtrate from the ammonium sulphate-precipitate, a strong biuret reaction was obtained, thus proving the presence of at least some unaltered peptone.

This experiment is almost a counterpart of one reported by Neumeister, and like his, testifies to the probability that the peptones formed in the alimentary tract, as a result of proteolysis, undergo retrogression through the agency of the epithelial cells of the intestinal walls during their absorption. I have tried similar experiments with deuteroproteose, notably with deuterocaseose, and have obtained corresponding results. The same method may be employed as that already outlined, although of course the deuterocaseose is in great part precipitated by saturation with ammonium sulphate. Still, this form of deuteroproteose, β deuterocaseose, as I have elsewhere noted, is very slowly precipitated by the ammonium salt. Consequently, it is an easy matter to demonstrate that this proteose, on treatment with the intestinal mucosa in the presence of blood at the body-temperature, is transformed into something completely and readily precipitable by ammonium sulphate; the filtrate from the latter failing to show any biuret reaction, although the corresponding control experiment without the intestine gives a bright violet color with cupric sulphate and potassium hydroxide.

Hence, we are certainly justified in saying that both peptones and proteoses undergo some retrogression when in contact with the walls of the intestine. Moreover, there is some evidence that the proteoses, before undergoing such a transformation, are first converted into peptone by the action of the intestinal walls, a statement which will apparently apply to both the primary and secondary proteoses. This primary action of the intestinal walls is not considered as due to any adherent trypsin, or to possible traces of succus entericus, but rather as a part of the action of the living epithelial cells, or perhaps as connected with the possible presence of lower organisms not removable from the intestinal wall by ordinary washing.

The transformation of peptones by the substance of the intestine is apparently common to the intestinal tract of many animals, and perhaps to all, and indeed can also be accomplished by the liver.[215] This latter fact is of some importance, since it adds weight to the supposition that this peculiar action of the intestine cannot be due to the possible presence of trypsin; a view which is strengthened by the fact that a glycerin-extract of the intestine has no action on amphopeptone. Certainly, the latter shows no diminution in the strength of the biuret reaction after long contact at body temperature with such an extract. Further, it has been shown that antipeptone, which is not affected by the pancreatic enzyme, suffers the same change as amphopeptone by contact with the intestine. Far more probable is it that retrogression or transformation of peptone by the substance of the intestine, is due to the vital activity of some or all of the epithelial cells of the intestinal mucosa; a characteristic possibly shared by some or all of the hepatic cells of the liver. The kidney-cells certainly do not possess this power, but we can see a special fitness in the liver-cells being endowed with the ability to quickly break down, or transform, any peptone or proteose that might by chance escape unaltered from the intestinal tract. Shore,[216] however, inclines to the view that the hepatic cells do not possess this power to any great extent, in opposition to the older views of Plòsz and Gyergai,[217] as well as of Seegen[218] and of Neumeister.

[215] Neumeister: Zeitschr. f. Biol., Band 27, p. 332.

[216] On the Fate of Peptone in the Lymphatic System, Journal of Physiol., vol. xi., p. 528.

[217] Ueber Peptone und Ernährung mit denselben, Pflüger’s Archiv f. Physiol., Band 10, p. 536.

[218] Zur Umwandlung des Peptons durch die Leber, _Ibid._, Band 37, p. 325.

With reference to the action of the stomach-mucosa on proteoses, it has been shown[219] that when relatively large amounts (5 grammes) are introduced into the stomach of a rabbit, the pylorus being ligatured, both proteoses and peptones may appear in the urine, thus indicating that while they may be absorbed to some extent under the above conditions, the proteoses are not readily transformed into native proteids without exposure to the intestine. Smaller amounts (2 grammes), however, may, under the above conditions, be completely transformed; at least Hildebrandt claims this to be the case, mainly on the ground that after the introduction of albumoses into the stomach, the pylorus being ligatured, no trace of them can be found in the urine. The same observer also claims that blood-serum, in the case of dogs, is able to transform albumoses into ordinary serum-globulin. Certainly, after intra-venous injection, proteoses disappear from the blood, but, as we shall see later on, a certain amount, at least, may be transferred to the lymph. It is also claimed that when albumoses are injected subcutaneously, neither albumoses nor peptones are to be detected in the urine. This, however, seems hardly probable in the light of what has been said, and especially in view of the fact that Neumeister’s experiments tend to show that even 0.1 gramme of albumoses introduced subcutaneously may give rise to temporary albuminuria.

[219] Hildebrandt: Zur Frage nach dem Nährwerth der Albumosen, Zeitschr. f. physiol. Chem., Band 18, p. 180.

Assuming for the moment that the chief products of proteolysis, _i. e._, the proteoses and peptones, are, during the act of absorption, transformed through the vital processes of the epithelial cells of the intestine into serum-albumin, or globulin, and absorbed as such into the blood, we may well consider whether such transformation, _i. e._, a retrogression into a native proteid again, is inconsistent, or out of harmony, with the general character of the changes known to occur in the body. In attempting to answer this question we need not look far to find a perfectly analogous case. Thus, in the digestion of starchy foods by the amylolytic ferments of both the saliva and the pancreatic juice, the carbohydrate material undergoes hydration with formation of dextrins and maltose, the latter, at least, being quickly absorbed into the circulating blood. But large quantities of sugar in the blood are certainly inimical to the well-being of the organism, and we find in the liver a tendency for the sugar to undergo a transformation, _i. e._, a retrogression into glycogen, either through simple dehydration or otherwise. Further, with reference to the possible conversion of proteoses into peptone by the substance of the intestine, we have a perfectly analogous case in the behavior of the intestinal mucous membrane toward maltose, the final product of amylolytic action. Thus, according to the recent work of M. C. Tebb,[220] the mucous membrane of the intestine has the power of transforming maltose into dextrose; simple warming at 40° C. of a solution of maltose in 0.5 per cent. sodium carbonate with a few grammes of the dried mucous membrane from the intestine, being sufficient to insure a marked conversion of maltose into the higher-reducing sugar, dextrose. This observation, I can confirm from experiments just completed in my own laboratory. This action is presumably due to a ferment, which, according to Tebb, is widely distributed throughout the body, being present not only in the intestine, but also in the liver, kidney, spleen, striated muscle-tissue, and, indeed, in the blood-serum; so that it would appear that nearly all the tissues of the body are endowed with the power of transforming maltose into dextrose. These statements being correct, it would seem that, while the amylolytic ferments of the several digestive juices transform, by hydrolytic action, starchy foods into maltose, the latter is exposed during its passage through the intestinal wall, as well as in the blood itself, to another ferment which carries the hydration still further, with formation of dextrose; and yet the latter product is destined, in part at least, to undergo retrogression into a starch-like body, _i. e._, glycogen, before it is completely utilized by the system. Thus, the analogy between these carbohydrate bodies and the products of proteolysis is complete, and we may well accept the statements already made regarding the ultimate fate of the proteoses and peptones formed during proteolysis, as in no way inconsistent with the general tenor of events going on in the body.

[220] On the Transformation of Maltose to Dextrose, Journal of Physiol., vol. xv, p. 421.

While we are inclined to believe that the chemical changes attending the absorption of proteoses and peptones occur mainly in the epithelial cells of the intestinal mucosa, and that there is a direct transference of the alteration-products to the blood, there are still other views that cannot be wholly ignored. Thus, the view originally advanced by Hofmeister,[221] in which special stress is laid upon the functional activity of the leucocytes of the adenoid tissue surrounding the intestine, demands some consideration. The theory supposes that these cells not only have the power of taking up peptones, but also of assimilating and transforming them into the cell-protoplasm. This view being correct, it is plain that the so-absorbed proteid must pass into the circulating blood through the thoracic duct, and Hofmeister further considers it probable that the lymph-cells of the mesenteric glands can transform any absorbed peptone that may escape the leucocytes of the adenoid tissue.

[221] Zeitschr. f. physiol. Chem., Band 4.

In apparent harmony with this view is the fact that the leucocytes in the adenoid tissue of the intestine are greatly increased in number during digestion.[222] Furthermore, it is a well authenticated fact that the proteoses or peptones found in pus are contained in the pus-cells themselves, and not in the fluid in which the corpuscles float.[223] In support of the first statement, Pohl,[224] in his recent study of the absorption and assimilation of food-stuffs, has emphasized the marked increase in the number of white blood-corpuscles in the circulating blood after the ingestion of proteid foods, especially such as meat, Witte’s peptone, and gelatin-peptone. It is to be noted further that the increase is most marked at about the third hour after the taking of food, viz., at a time when digestive proteolysis would naturally be at its height. Moreover, the maximal increase, according to Pohl’s data, is astounding, amounting as it does in many cases to a hundred per cent. Thus, in one instance, in the case of a dog, the number of white blood-corpuscles per cubic millimetre of blood was 8,689; yet two hours after the feeding of 100 grammes of meat the number increased to 17,296 per cubic millimetre, followed six hours after by a return to the original figure.

[222] Arch. f. Exp. Pathol. u. Pharm., Band 20 and Band 22.

[223] Zeitschr. f. physiol. Chem., Band 4, p. 268.

[224] Arch. f. Exp. Pathol. u. Pharm., Band 25, p. 31.

This indicates the general tenor of Pohl’s results, which have been taken, by some physiologists at least, as confirmatory of Hofmeister’s views; the interpretation naturally being that digestive proteolysis in the alimentary tract is accompanied by a rapid production of new leucocytes in the lymph-spaces surrounding the intestine, and followed by a rapid transference of the corpuscles from their point of origin to the circulating blood, from which they gradually disappear as their material is made use of in the different parts of the body. In harmony with this view, Pohl finds that there is a much larger number of leucocytes in the blood and lymph flowing from the intestine of an animal in full digestion, than in the arterial blood coming to the intestinal tract. Further, when due consideration is given to all the circumstances attending the circulation of the blood through the abdominal organs, in connection with the great increase in the number of leucocytes during digestive proteolysis, it seems not unreasonable to suppose that some proteid matter might be transferred from the intestine to the blood during the digestive period of six or eight hours. Moreover, if Pohl’s views are correct, we see that a portion, at least, of the proteid food-product may be transformed into organized material in the body of the lymph-cell prior to its passage into the blood, thus harmonizing with the statement already made regarding the utter lack of proteoses and peptones in the blood and lymph. This obviously means an upbuilding of the ordinary products of digestive proteolysis into the living protoplasm of the leucocytes in the intestinal walls, implying, however, that the transformation is accomplished solely by the leucocytes themselves, and not by the epithelial cells of the intestine.

I have given this brief summary of Pohl’s work because it is so closely in harmony with the original views of Hofmeister, and because it offers an easy explanation of one possible way in which some of the products of digestion might perhaps pass from the intestine into the blood. I am inclined to believe, however, that the so-called digestive leucocytosis, which unquestionably does exist, is not a direct result of digestive proteolysis in general, but rather an indirect result, coming from the stimulating action of the nuclein, contained especially in animal cells. Thus, it is a significant fact, as Pohl himself reports, that wheat-bread, with its fairly large amount of proteid matter, and which is fully capable of nourishing the animal body, fails to exert any influence on the number of leucocytes in the blood. Yet we know that the gluten and other proteids of wheat-flour are converted by digestive proteolysis into proteoses and peptones, with the same general properties as like products of animal origin.

In this connection we may note the experiments of Horbaczewski,[225] which show that nuclein administered to a healthy man will give rise to a very marked increase in the number of leucocytes in the blood. Thus, a few grammes of nuclein may produce as striking a condition of leucocytosis as a large amount of proteid food, due no doubt to proliferation of the lymphoid elements of all the lymphatic tissues of the body. Horbaczewski has reported that the mere injection of 0.25 gramme of nuclein, in the case of rabbits, will cause marked enlargement of the spleen, with striking karyokinetic changes. Hence, it may be assumed that whenever nuclein is set free in the body, leucocytosis may result, provided the nuclein passes into the circulation and is not decomposed immediately after its liberation.

[225] Monatshefte f. Chemie, Band 12, p. 246.

These facts, it appears to me, offer a more consistent line of 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