intestinal tract can be recognized with the naked eye. Their eggs must be looked for with the microscope.

Tape-worms.-It is not always easy to recognize the kind of tape-worm by a single segment passed with the feces, because the uterus, which furnishes the most characteristic

points of difference, is not developed in the young segments and is atrophied in the old ones. When the whole worm is obtained the problem is much simpler. The uterus is best made out by squeezing a segment between two slides and

holding it up to the light. The heads are examined under the microscope in water, salt solution, or glycerin.

Tænia Solium (Fig. 92).-Head has four suckers and a

circle of hooklets; uterus is noticeably but little branched. The genital tract opens laterally. The eggs develop into the cysticerci cellulose, which are not infrequently found in man.

FIG. 95.-Bothriocephalus latus: A, head; B, ripe joint, x 6; C, egg of bothriocephalus latus (Heller); D, egg with developed embryo (Leuckart).

The scolex is obtained for examination by tearing open the cyst and examining the inner wall. The suckers and hook

lets are best studied after mounting fresh and pressing under

a cover-glass.

Tænia Mediocanellata s. Saginata (Fig. 93).-Head has four strong suckers, but no hooklets; uterus is very much branched, segments show marked muscular development. The genital tract opens laterally. The eggs develop into cysticerci, which do not occur in man.

Tænia Echinococcus (Fig. 94) occurs in dogs. The echinococcus cysts which occur in man are recognized by the very characteristic laminated structure of the cyst-wall. The heads of the scolices have four suckers and a double circle of hooklets.

Bothriocephalus Latus (Fig. 95).-The opening of the

FIG. 99.-Comparative size of eggs of intestinal parasites: a, tænia solium; b, tænia mediocanellata; c, ascaris lumbricoides; d, trichocephalus dispar; e, oxyuris vermicularis (after Strümpell).

genital tract lies in the median line. The head is flattened, and has two small suckers situated at the sides.

SPECIAL STAINS FOR CERTAIN TISSUE-ELEMENTS OTHER THAN NUCLEI.

MASTZELLEN.

MASTZELLEN are found in the connective tissue, more especially in chronic inflammatory processes. Their protoplasmic granules stain intensely like bacteria with the basic aniline dyes. Several methods of staining the granules are given. With Unna's stains for plasma-cells a differential color-stain is obtained for the granules of the mastzellen. Ehrlich's Method.-A. General Stain.-Harden in al

cohol.

1. Stain with a saturated aqueous solution of dahlia.

2. Wash out with acidified water.

3. Dehydrate in alcohol; clear and mount in Canada balsam.

B. Specific Stain.-Only the protoplasmic granules are stained. Harden in alcohol.

2. Wash out in alcohol, clear, and mount.

C. Ehrlich-Westphal Method.-Nuclei red; granules blue. Harden at least a week in alcohol.

1. Stain in the following solution twenty-four hours: Alum-carmine solution,

200;

Saturated solution of dahlia in absolute alcohol, 200;
Glycerin,

Glacial acetic acid,

100;

20.

(Stir repeatedly, then allow the mixture to stand for some time.)

2. Decolorize for twenty-four hours in absolute alcohol. 3. Oil, Canada balsam.

Unna's Isolated Stains for Mastzellen.-Harden in alcohol.

A.-1. Stain in polychrome methylene-blue solution, plus a little alum, for three hours to over-night.

2. Wash in water.

3. Absolute alcohol, oil of bergamot, balsam.

B.-1. Stain in polychrome methylene-blue solution onequarter of an hour.

2. Wash in water.

3. Decolorize in glycerin-ether mixture for five to ten minutes.

4 Wash a long time in water.

5. Absolute alcohol, oil, balsam.

PLASMA-CELLS.

These are certain cells, much studied by Unna, which are very abundant in subacute and chronic pathological processes, and which are characterized by a protoplasm that stains quite deeply in alkaline methylene-blue solutions. The two methods best suited for their demonstration furnish at the same time a differential color-stain for mastzellen. The granules of the latter are stained red, the plasma-cells are stained blue.

Unna's Differential Stains for Plasma-cells and Mastzellen. Harden tissues in absolute alcohol.

A.—1. Stain paraffin sections in polychrome methyleneblue one-quarter of an hour to over-night.

2. Decolorize in a small dish of water, to which are added a few drops of glycerin-ether mixture.

3. Wash thoroughly in water.

4. Absolute alcohol, oil of bergamot, balsam.

B.-1. Stain in polychrome methylene-blue solution five to fifteen minutes.

2. Wash in water.

3. Decolorize and dehydrate in a per cent. alcoholic solution of neutral orcein (about fifteen minutes). 4. Absolute alcohol, oil of bergamot, balsam.

CONNECTIVE-TISSUE FIBRILLÆ.

Van Gieson's picro-acid-fuchsin solution is much employed for staining connective-tissue fibrillæ, but is much better adapted for the coarse than for the fine fibrillæ, which it often fails to stain sharply. The proportions given are those recommended by Freeborn. Occasionally it will be found necessary to increase the proportion of the acid-fuchsin.

1. Harden in chrome salts or in corrosive sublimate. The results after alcohol are not so good.

2. Stain deeply in alum-hematoxylin. 3. Wash in water.

4. Stain for three to five minutes in

I per cent. aqueous solution of acid fuchsin,
Saturated aqueous solution of picric acid,

5 c.c.

100

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