Text book of veterinary medicine, Volume 2 (of 5)

by James Law

The morbific agent must be sought in some source from which it can be supplied with great rapidity under the stimulus of a short but active exertion. The chylopoietic viscera furnish such a source. The healthy liver contains one-fourth of the entire mass of the blood. The torpid congested liver of the vigorous high conditioned horse, after a short period of idleness, on full, rich feeding, must hold much more than this normal ratio. The spleen, the natural store-house or safety valve of the portal veins, is also gorged with this liquid in the high fed, idle animal. This organ which is always turgescent after meals, is especially so in the over-fed horse, which for twenty-four hours has been denied the opportunity of working off by exercise, the superfluous products of an active digestion and absorption. Then the whole of the portal veins and the capillaries in which they originate are surcharged with rich blood which cannot make its way with the necessary dispatch through the inactive liver.

In this condition there is incomparably more than a quarter of the entire mass of blood, enriched to the highest degree in proteids, ready to be discharged through the liver and hepatic veins into the general circulation. Under the action of the hurried breathing and circulation, caused by the sudden and active exertion, this whole mass of rich blood is speedily unloaded on the right heart, the lungs and the systemic circulation. One can hardly conceive of a more effective method of inducing a sudden plethora, with an excess of both globules and albuminoids.

The presence of actual poisons in such blood is not so easily certified.

The absorption of bile elements and especially of taurocholic acid, which is a solvent of the red blood globules, and would set free their globulin might account for the characteristic condition of the blood. The powerful aspiratory action of the chest, would speedily empty the whole of the liver blood vessels, and lessening their tension below that of the biliary radicals would determine an active absorption of bile or of the more diffusible of the bile elements. A manifest objection to this view is the absence of an icteric tint in the mucous membranes of the affected animals. The visible mucosæ are of a brownish red hue, such as might come from hæmoglobin dissolved in the blood serum, rather than the yellow tint which might be expected from bile pigment. The theory of poisoning by bile acids therefore, would require an explanation of concurrent suppression or decomposition of the bile pigments.

Other sources, however, offer solvents for hæmoglobin, benzoic acid, which is derived from a cellulose in the fodders, and forms the source of hippuric acid, dissolves red globules (Landois). In the over-fed horse with active digestion, but inactive body and liver, this must accumulate in the liver, spleen and portal system, and when suddenly drawn into the blood without time for oxidation in the liver it will contribute to the condition of hæmoglobinæmia.

Peptones, being very diffusible, are very rapidly absorbed, but they are not found, in healthy conditions, in the portal vein (Neumeister). These are manifestly transformed into albumen in the intestinal mucosa (Salvioli), or taken up by the very numerous leucocytes and transformed or carried elsewhere (Hoffmeister). But peptones injected into the blood of the dog render it incoagulable, and in large quantity are fatal (Landois). An excess of glycogen dissolves the red globules, and the conditions of heavy feeding and torpid liver, are calculated to produce this in great excess and to store it in the liver cells.

Under the extra vigorous aspiratory force of the chest, these highly diffusible agents, present in great excess, are likely to be drawn on through the mucosa, into the portal vein, liver, and cava, without an opportunity for complete transformation by leucocytes or liver cells. These would tend to rob the blood globules of their normal physiological vigor, would unfit them for maintaining the healthy functions of lungs, kidneys, brain or muscle, and would unfit the globules for successful resistance to solvents and other inimical influences.

Again it is an important function of the liver, spleen and red bone marrow to disintegrate worn out or abnormal red globules. These are taken up by the white blood corpuscles of the hepatic capillaries, by the cells of the spleen and the bone marrow and are stored up chiefly in the capillaries of the liver, in the spleen, and in the marrow of bone. They are transformed, partly into colored and partly into colorless proteids, and are either deposited in the granular form, or are dissolved (Landois). Quincke says: “That the normal red blood globules and other particles suspended in the blood stream are not taken up in this way, may be due to their being smooth and polished. As the corpuscles grow older and become more rigid, they, as it were, are caught by the amœboid cells. As cells containing blood corpuscles are very rarely found in the general circulation, one may assume that the occurrence of these cells within the spleen, liver, and marrow of bone, is favored by the slowness of the circulation in these organs.” From this chain of normal processes of blood disintegration, we may reasonably infer, a greatly exaggerated work of blood destruction when, in connection with an increased density of the plasma, and the presence in the portal blood of poisonous products of digestion, the red globules have been altered in density, in outline and in vitality, so that they become ready victims of the amœboid cells of blood and tissues. Then the stagnant condition of this altered blood in the compulsorily idle animal favors the greatest excess of this destruction and the storing up of an increased quantity of hæmoglobin and other products, to be poured suddenly into the general circulation as soon as the movement of the blood is quickened by exercise.

This destruction of the red blood globules by disintegration contributes to the formation of numerous decomposition-products, like succinic, formic, acetic, butyric and lactic acids, inosite, leucin, xanthine, hypoxanthin, and uric acid, some of which are strongly toxic. The tendency will be to lower the vitality of the red globules and thus to render them the easier victims of the leucocytes and of the liver, spleen and marrow cells. Even the freed hæmoglobin appears to exert a solvent action on the red blood globules. These are, of course, most concentrated and effective in the seat of their production, yet when drawn suddenly in large amount, into the general circulation, by the vigorous aspiratory action of the chest, they may prove seriously detrimental to the blood at large.

Again a variety of toxic matters are introduced into the system in the food and others are developed from the food in the stomach and intestine. Brieger found in the gastric peptones a potent alkaloid having the effect of urari, and which in excess would determine muscular paralysis. The alkaloidal and other poisons produced by fermentations in the intestines have to be safely disposed of. The ptomaines, if not too abundant, are arrested or even decomposed in the liver which thus stands as a guardian, at the outlet of the portal system, to protect the body at large. But this antitoxic function of the liver is only exercised in the presence of glycogen (Rogers, Landois), and forced muscular movement soon removes all glycogen from the liver of the dog (Landois). Again glycogenesis in the liver is now believed to be dependent on a ferment produced by the pancreas. If therefore, the sudden active exercise and the aspiratory action of the chest freed the liver of its glycogen, and hurried the alkaloidal and other poisons through its capillaries too rapidly to allow of the protective action of the liver cells, or if the pancreas as well as the liver had become torpid and had failed to produce the requisite amount of glycogen-ferment for the liver, the poisoning of the blood and system at large would be imminent.