pigment from the liver by the normal channels be prevented, as
by obstruction of the main bile ducts, the bile will accumulate
until it regurgitates or is absorbed into the lymph and blood
vessels, and is carried in a soluble state throughout the tissues,
thus producing a general staining—an essential characteristic of
jaundice.
3. In extraneous pigmentation we have coloured substances either in a solid or fluid state, gaining entrance into the organism and accumulating in certain tissues. The channels of entrance are usually by the respiratory or the alimentary tract, also by the skin. Pneumonokoniosis is due to the inhalation of minute particles of various substances—such as coal, stone, iron, steel, &c. These foreign particles settle on the lining membranes, and, by the activity of certain cells (fig. 50, Pl. V. and fig. 30, Pl. III.), are carried into the tissues, where they set up chronic irritation of a more or less serious nature according to the nature of the inhaled particles.
Certain metallic poisons give rise to pigmentation of the tissues, e.g. in the blue line on the gums around the roots of the teeth due to the formation of lead sulphide, or in chronic lead poisoning, where absorption may have taken place through the digestive tract, or, in the case of workers in lead and lead paints, through the skin. Prolonged ingestion of arsenic may cause pigmentary changes in the skin. If silver nitrate salts be administered for a long period as a medication, the skin that is exposed to light becomes of a bluish-grey colour, which is extremely persistent. These soluble salts combine with the albumins in the body, and are deposited as minute granules of silver albumin are in the connective tissue of the skin papillae, serous membranes, the intima of arteries and the kidney. This condition is known as argyria.
Various coloured pigments may be deposited in the tissues through damaged skin surface—note, for example, the well-known practice of “tattooing.” Many workers following certain occupations show pigmented scars due to the penetration of carbon and other pigments from superficial wounds caused by gunpowder, explosions, &c.
Hyaline.—This term has been applied to several of the transparent homogeneous appearances found in pathological conditions. It is now commonly used to indicate the transparent homogeneous structureless swellings which are found affecting the smaller arteries and the capillaries. The delicate connective-tissue fibrillae of the inner coat of the arterioles are usually first and most affected. The fibrils of the outer coat also show the change to a less extent, while the degeneration very rarely spreads to the middle coat. This swelling of the walls may partly or completely occlude the lumen of the vessels.
Hyaline degeneration is found in certain acute infective conditions; the toxins specially act on these connective-tissue cell elements. It also seems to be brought about by chronic toxaemias, e.g. in subacute and chronic Bright's disease, lead poisoning and other obscure conditions. The hyaline material, unlike the amyloid, does not give the metachromatic staining reactions with methylene-violet or iodine. The chemical constitution is not certain. The substance is very resistant to the action of chemical reagents, to digestion, and possibly belongs to the glyco-proteids.
Amyloid.—The wax-like or amyloid substance has a certain resemblance to the colloid, mucoid and hyaline. It has a firm gelatinous consistence and wax-like lustre, and, microscopically, is found to be homogeneous and structureless, with a translucency like that of ground-glass. Watery solution of iodine imparts to it a deep mahogany-brown colour; iodine and sulphuric acid occasionally, but not always, an azure-blue, methyl violet, a brilliant rose-pink and methyl-green gives a reaction very much like that of methyl-violet, but not so vivid. The reaction with iodine is seen best by direct light; the reactions with the other substances are visible only by transmitted light. The name “amyloid” was applied to it by Virchow on account of the blue reaction which it gives occasionally with iodine and sulphuric acid, resembling that given with vegetable cellulose. It is now known to have nothing in common with vegetable cellulose, but is regarded as one of the many albuminoid substances existing in the body under pathological conditions. Virchow's conjecture as to the starchy nature of the substance was disproved by Friedrich and Kekule, who confirmed Professor Miller's previous finding as to its albuminous or protein nature. Oddi in 1894 isolated from the amyloid liver a substance which Schmiedeberg had previously obtained from cartilage and named “chondroitinic-sulphuric acid” (Chondroitinschwefelsäure). It also occurs in bones and elastic tissue, but is not present in the normal human liver. Oddi does not regard it as the essential constituent of amyloid, chiefly because the colour reactions are forthcoming in the residuum after the substance has been removed, while the substance itself does not give these reactions. Quite likely the amyloid may be a combination of the substance with a proteid. The soda combination of the acid as obtained from the nasal cartilage of pigs had the composition C18H25Na2NSO17.
Krawkow in 1897 clearly demonstrated it to be a proteid in firm combination with chrondroitin-sulphuric acid. As probably the protein constituent varies in the different organs, one infers that this will account for the varying results got from the analysis of the substance obtained from different organs in such cases.
This amyloid substance is slowly and imperfectly digested by pepsin—digestion being more complete with trypsin and by autolytic enzymes.
There is no evidence that this material is brought by the circulating blood and infiltrates the tissues. It is believed rather that the condition is due to deleterious toxic substances which act for prolonged periods on the tissue elements and so alter their histon proteins that they combine in situ with other protein substances which are brought by the blood or lymph.
Amyloid develops in various organs and tissues and is commonly associated with chronic phthisis, tubercular disease of bone and joints, and syphilis (congenital and acquired). It is known to occur in rheumatism, and has been described in connexion with a few other diseases. A number of interesting experiments, designed to test the relationship between the condition of suppuration and the production of amyloid, have been made of late years. The animal most suitable for experimenting upon is the fowl, but other animals have been found to react. Thus Krawkow and Nowak, employing the frequent subcutaneous injection of the usual organisms of suppuration, have induced in the fowl the deposition within the tissues of a homogeneous substance giving the colour reactions of true amyloid. When hardened in spirit, however, the greater part of this experimental amyloid in the fowl vanishes, and the reactions are not forthcoming. They were unable to verify any direct connexion between its production and the organism of tubercle. These observations have been verified in the rabbit, mouse, fowl, guinea-pig and cat by Davidsohn, occasionally in the dog by Lubarsch; and confirmatory observations have also been made by Czerny and Maximoff. Lubarsch succeeded in inducing it merely by the subcutaneous injection of turpentine, which produces its result, it is said, by exciting an abscess. Nowak, however, found later that he could generate it where the turpentine failed to induce suppuration; he believes that it may arise quite apart from the influence of the organisms of suppuration, that it is not a biological product of the micro-organisms of disease, and also that it has nothing to do with emaciation. It is a retrogressive process producing characteristic changes in the fine connective tissue fibrils. The change appears to begin in the fibrils which lie between the circular muscle fibres of the middle coat of the smaller arterioles and extends both backwards and forwards along the vessels. It spreads forwards, affecting the supporting fibres outside the epithelium of the capillaries, and then passes to the connective-tissue fibrils of the veins. The secreting cells never show this change, although they may become atrophied or destroyed by the pressure and the disturbance of nutrition brought about by the swollen condition of the capillary walls. The circulation is little interfered with, although the walls of the vessels are much thickened by the amyloid material (fig. 51, Pl. V.).
Amyloid Bodies.—These are peculiar bodies which are found in the prostate, in the central nervous system, in the lung, and in other localities, and which get their name from being very like starch-corpuscles, and from giving certain colour reactions closely resembling those of vegetable cellulose or even starch itself. They are minute structures having a round or oval shape, concentrically striated, and frequently showing a small nucleus-like body or cavity in their centre. Iodine gives usually a dark brown reaction, sometimes a deep blue; iodine and sulphuric acid almost always call forth an intense deep blue reaction; and methyl-violet usually a brilliant pink, quite resembling that of true amyloid. They are probably a degeneration-product of cells.
Spurious Amyloid.—If a healthy spinal cord be hung up in spirit for a matter of six months or more, a glassy substance develops within it quite like true amyloid. It further resembles true amyloid
