suggesting papillomata, are observed (Fig. 139). Section through these shows that they consist of proliferated cells with enlarged

blood-vessels, from which the adult worm may be removed. The tissues surrounding the vessels may contain eggs in enormous numbers. The mucous membrane is frequently covered with a calcareous deposit composed of urate and oxalate of sodium, and the excrescences may be converted into calcified polyps. Among the final results may be cicatricial strictures of the ureter, pyelitis, and distention of the pelvis of the kidney, with atrophy of the kidney-substance. Similar pathologic processes may be found in the rectum. When the portal vein is occupied the eggs of the distoma may be abundant in the liver-substance. Distoma hematobium is a parasite occurring with enormous frequency in Northern Africa and neighboring countries. It is compara

FIG. 139.-Papillary thicken- tively rare in other parts of the world.

ing of the mucous membrane

of the bladder, showing distoma-eggs in sitú (Mosler and Peiper).

DISTOMA PULMONALE.

This organism is from 8 to 10 mm. in length and from 5 to 6 mm. in breadth. The eggs are brownish, and from 0.08 to 0.1 mm. in length. The worm occurs in the lungs, occupying excavated spaces, usually near the periphery of the organ. These cavities contain reddish or quite hemorrhagic mucopurulent liquid and abundant eggs. The cavities are in communication with the bronchi, and clinically the disease is marked by cough and hemorrhagic expectoration or even repeated hemoptysis. This parasite occurs very frequently in Japan, China, and Corea.

OTHER FLUKE-WORMS.

Among other forms of distoma of less importance are Distoma crassum, met with a few times in the intestine; Distoma heterophyes; Distoma ophthalmobium, found in the lens of the eye; Distoma sinese, found in the liver; Distoma conjunctum, also occurring in the liver; and the Monostoma lentis, occurring in the eye. Amphistoma hominis occurs in the intestinal tract. Two forms, the Hexathyridium venarum and Hexathyridium pinguicola, are possibly forms of encapsulated Distoma hepaticum.

ANNELIDES.

The

Two forms of leeches are of some pathologic importance. The Hirudo Ceylonica is a form occurring with great frequency in Ceylon and other islands and in parts of South America. It is

found in vegetation, and attaches itself to the skin of the legs and to other parts of man by means of a sucker and its short teeth. It may give rise to painful ulcerations when removed. The Hirudo vorax is met with in parts of Europe and Africa. It gains access to the mucous membranes of the mouth, larynx, trachea, or nasal chambers, and leads to inflammatory troubles. It is not able to effect a lodgement upon the skin.

ARTHROPODIA.

A number of parasites belonging to the groups Arachnoidea and Insecta are met with in man. Most of these, however, are purely external parasites, and are fully described in works upon diseases of the skin. There are two forms, however, that merit brief description here: the Pentastomum denticulatum, the larval form of Pentastomum tænioides; and the larvæ of various flies, the presence of which in the gastro-intestinal tract and other parts of the body is termed myiasis.

PENTASTOMUM DENTICULATUM.

This parasite is occasionally found in the liver and rarely in the spleen, intestinal walls, lungs, and kidneys of man. It is discovered in small nodular lesions, which consist of the more or less degenerated parasite lying in a cheesy or semicalcified material, surrounded by a fibrous or calcareous capsule. The parasite is from 4 to 5 mm. in length and 1.5 mm. in breadth; has a rather rounded body, which is encircled by parallel rings armed with spicules; and is provided with two pairs of stout chitinous hooklets, one pair lying on either side of the mouth. The adult form, Pentastomum tanioides, resembles its larva in structure, but is considerably larger, the male being from 16 to 18 mm. long, the female from 60 to 85 mm. This form lodges in the nasal cavities and frontal sinuses of the dog and other animals, and produces eggs containing the embryos, which escape with the nasal secretion and eventually gain access to the alimentary tract of other animals or of man.

MYIASIS.

A number of flies, of the orders Estridæ, Musca, Lucilia, and Sarcophaga, may deposit their eggs in wounds or in cavities of the body to which they gain access, such as the nasal or pharyngeal chambers and the communicating passages. The eggs so deposited are hatched, and the larval insects may be retained and may occasion intense irritation. Sometimes the larvæ are found in the gastro-intestinal tract, the eggs having been swallowed with food. Immense numbers may be discharged from the intestines, and in some cases the larvæ seem to occasion intestinal irritation. The term myiasis is given to the invasion of these larval insects.

PART II.

SPECIAL PATHOLOGY.

CHAPTER I.

DISEASES OF THE BLOOD.

ANATOMY.

THE blood is a liquid tissue composed of corpuscles or cells and a fluid intercellular substance. The cells are of three kinds : the red corpuscles, or erythrocytes; the white corpuscles, or leukocytes; and the blood-plaques, or hematoblasts. The fluid element of the blood, the liquor sanguinis, or plasma, is an albuminous and saline liquid of a slightly varying composition. The blood as a whole is red in color, rather viscid, and alkaline in reaction. The total quantity is about one-thirteenth of the body-weight.

The

The erythrocytes, or red corpuscles, are biconcave disks about 7 in diameter and having a yellowish or amber color. They are quite uniform in size and regularly rounded. Histologically they are composed essentially of an albuminous substance containing hemoglobin embedded in a delicate stroma. hemoglobin is the important element, and constitutes 95 per cent. by weight of the corpuscles. In early fetal life most of the red corpuscles are nucleated, but the nucleated forms later decrease in number and are comparatively scanty at the time of birth. Within the first few months of post-fetal life all of them disappear, and in subsequent years nucleated corpuscles are present only in cases of disease.

There are about 5,000,000 corpuscles in the cubic millimeter of the blood of normal individuals. The figures vary slightly at different times in the same individual, and many influences contribute to the production of more lasting changes in number (see page 327). The volume of the red corpuscles in the blood is dependent upon the number of corpuscles and upon their size. Observers have reached varying results in studying the volume, but it may be placed at between 40 and 50 per cent. of the total bulk of the blood.

The leukocytes, or white corpuscles, are rounded or spherical bodies presenting a more or less granular appearance in

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the fresh state. They vary in size from the diameter of the red corpuscles to several times the size of the latter. The leukocytes are identical with the lymph-corpuscles. They are of several more or less distinct varieties; the classification, however, is exceedingly difficult, as transitional forms are abundant. The classification most frequently adopted is that of Ehrlich and of his pupils, and while it is not entirely satisfactory, it has one advantage over others, viz., that of simplicity. Ehrlich distinguishes (Fig. 140):

FIG. 140-Various forms of blood-corpuscles: a, lymphocyte; b, lymphocyte approaching c; c, large mononuclear; d, transitional; e, polymorphonuclear neutrophile; f, polymorphonuclear eosinophile; g, broken eosinophile; h, neutrophilic myelocyte; i, eosinophilous myelocyte; j, basophile, mast-cell; k, red corpuscles; 7, nucleated red corpuscles.

1. Small mononuclear leukocytes, or lymphocytes. These are smaller than the red corpuscles, or about the same size, are spherical, and contain a relatively large nucleus, the protoplasm often forming a scarcely visible band around the nucleus. The latter is rich in chromatin and stains deeply. Sometimes cells considerably larger than the typical lymphocyte may resemble them in other respects, and it may be difficult to determine whether these are lymphocytes or large mononuclear cells (Fig. 140, b). The protoplasm of lymphocytes normally contains no granular matter when stained by the ordinary methods. Deep staining with methyleneblue with the aid of heat does, however, frequently lead to the detection of a slightly granular character in the protoplasm.

2. Large mononuclear leukocytes. These forms are larger than the lymphocytes, being from two to three times the diameter of the red cells. They are often oval in outline, and the nucleus is poorer in chromatin than that of the lymphocyte, so that it appears comparatively pale in the stained blood. The protoplasm is usually free of granules, but it may show fine and very pale granules when stained with intense basic stains like methylene-blue.

3. Transitional leukocytes. These are similar to the last, but

differ in that the nucleus is often a little indented or horseshoeshaped. It is very often impossible to determine satisfactorily whether a certain cell is a large mononuclear or a transitional form, and the two may be considered as practically the same. The protoplasm, as a rule, contains no granules, but neutrophilic granules (see page 315) have occasionally been detected, and eosinophile granules are more frequently present.

4. Polymorphonuclear leukocytes; polynuclear leukocytes; neutrophiles. These are the most numerous forms, and probably represent the fully developed white blood-cell. They are somewhat smaller than the large mononuclear elements, and are distinguished by a polymorphous nucleus which is richer in chromatin than that of the large mononuclear form, though perhaps less rich than that of the lymphocyte. The nuclei are elongated, and variously curved or distorted so as to resemble the letters S, U, V, Z, etc., and in some cases they are wreath-shaped. Frequently parts of the nucleus are so thin that they are scarcely visible, or actually become broken, and the term polynuclear was therefore applied. This name is, however, less appropriate than the term polymorphonuclear. The amount of chromatin in the nucleus varies greatly, and the size of the nucleus is correspondingly variable. The protoplasm usually contains fine granules, which are closely set and almost completely fill the cell. These granules have a strong affinity for neutral mixtures of anilin or other stains, and have therefore been called the neutrophilic granules (see page 315). A small proportion of the polymorphonuclear leukocytes of the blood contain eosinophile granules. These cells are usually larger than the neutrophilic forms, and the nucleus is more nearly like that of the typical transitional leukocyte.

5. Myelocytes. These are large cells identical with the large granular cells of the bone-marrow. They are often three or four times the size of the red corpuscles, and are distinguished by a large, pale, oval nucleus. The protoplasm usually contains neutrophilic granules, but occasionally contains eosinophile granules. The nucleus is frequently somewhat irregularly outlined and not rarely suffers degenerative change. Smaller cells, resembling the typical myelocyte in the character of the nucleus and protoplasm, are sometimes observed, and are difficult to classify. Myelocytes occur in exceedingly small numbers, if at all, in normal blood. They are abundant in certain forms of leukemia, and also occur in pernicious anemia and various infectious and systemic diseases.

The granules of the leukocytes are classified according to their behavior with the anilin stains. We may distinguish four important types of granules (Figs. 140 and 141):

1. a-granules, eosinophile granules, or oxyphile granules. These are coarse granules giving the appearance in the unstained blood