Outlines of practical histology

globules. The active gland presents some resemblance to a salivary gland, so closely are the alveoli pressed together, with only a small quantity of interstitial connective tissue between them. The acini are in groups and separated from each other by fibrous imperfect

FIG. 365.-T.S. Mammary Gland.

D. Duct; A. Group of acini with much connective tissue between, X 20

septa. Numerous corpuscles, including granular cells, occur in the alveolar connective tissue. The ducts are lined by columnar epithelium, and in a section of a human gland they appear large.

(i.) Harden small parts of the mammary gland in absolute alcohol. Select, when possible, the gland of a recently pregnant woman (or animal). Stain the sections in hæmatoxylin and mount

in balsam, i.e., to get a general view of the gland structure. Stain

in bulk, embed and cut in paraffin.

(ii.) Harden very small pieces of a fresh gland, e.g., from a

pregnant cat or rabbit, in Flemming's mixture and stain the sections (very thin) in safranin.

1. V.S. Mammary Gland (Haematoxylin) (L and H) (fig. 365). (a.) Observe the groups of acini, separated by a relatively large

amount of somewhat loose connective tissue, and sections of the ducts (D). The sections should be made so as to include the nipple, when the larger ducts with their dilations will be seen. The ducts are large between the lobules, and within the latter the course of the finer ducts can readily be traced.

(b.) The globular acini, with a basement membrane lined by a single layer of somewhat flattened or cubical epithelium. In the inter-alveolar tissue many leucocytes and granular cells.

2. Active Mammary Gland (Safranin) (H).

(a.) Study specially the acini. Observe the large and tall columnar cells lining the acini, and in some of the cells clear refractive granules of fat. The lumen is wide, and is usually partially filled with the debris of the secretion-milk. Osmic acid is a good agent for showing the presence of fatty granules (fig. 366).

3. Colostrum (H), i.e., the first milk secreted after delivery. If this can be obtained, examine it, and note, in addition to the ordinary milk-globules (Lesson I. 3), large coarsely granular nucleated refractile cells-colostrum corpuscles. The granules are sometimes pigmented, and are fatty (fig. 367).

UMBILICAL CORD AND PLACENTA.

4. T.S. Umbilical Cord.-Harden this in Müller's fluid or alcohol. Make T.S. by freezing, and stain them with hæmatoxylin. or picro-carmine. Methyl-violet is also a good stain.

(a.) Note on the outside of

the circular mass of tissue a thin layer of flattened cells derived from the amnion.

(b.) The cord itself, composed of Wharton's jelly, enclosing usually two umbilical arteries and a single vein with very thick muscular coats. They are completely surrounded by Wharton's jelly, which, however, in a cord at full time is very largely composed of fibrous tissue. Still numerous branched

connective tissue corpuscles exist FIG. 368.-Human Placenta Villi. Blocdin the meshes, and there are

vessels black.

also present numerous lymphoid-looking cells (Lesson XII. 10).

5. Fresh Placenta (H).--Tease a fragment of a placenta in normal saline. Note the villi, each long, tapering, and branched. In the interior capillary loops which occupy the greater part of the

villus, so that only a small amount of connective tissue intervenes between the vessels. Each villus is covered on its surface by a layer of epithelium, which, however, is thin at one part and thick at another. Especially at the ends of the villi are large granular masses of protoplasm containing many nuclei, but one cannot make out a separation of these masses into cells. They often contain vacuoles. The arangement of the blood-vessels may be followed from the distribution of the blood-corpuscles (fig. 368).

Small portions of a placenta are also to be hardened in Müller's fluid and stained in bulk in borax-carmine. Individual villi may be isolated in dilute alcohol or osmic acid.

6. Injected Placenta.-Examine a vertical section of a placenta with the foetal blood-vessels injected, say blue, and the maternal vessels red. Observe how the one set interlocks with the other, yet both systems are closed and do not communicate with each other.

LESSON XXXVIII.

TO MAKE PREPARATIONS RAPIDLY FROM
FRESH TISSUES.

Ir is of the utmost importance that the student should be acquainted with the methods of making preparations from fresh tissues placed in his hands. The following is an outline of the work that each one can readily do for himself if supplied with a pithed frog, or other suitable material.

A. From a Frog.

1. Corneal Corpuscles. With a sharp pair of scissors cut out the cornea. Divide it into two parts.

(a.) Treat one by the lemon-juice method (p. 79).

(.) Treat the other part by placing it direct into .5 per cent. AuCl (half an hour); wash in distilled water; place in

a saturated solution of tartaric acid at 50° C. until the gold becomes reduced (p. 79).

(c) A cornea may be placed fresh in dilute methylene-blue (1300 normal saline). Mount in picrate of ammonia glycerine (p. 192).

2. Corneal Lymph-Spaces.-Remove the eyelids, expose the surface of the other cornea, scrape off the epithelium, and rub it

with solid silver nitrate. Cut out the cornea and expose it to light

in water (p. 77).

3. Tendons.--These are best made from the tarsal tendons, which can readily be snipped off in considerable lengths.

(a.) Fibrils.-Tease a piece in baryta-water and mount in glycerine.

(b.) Tendon Cells.—(i.) Add dilute acetic acid to bring into view the rows of cells, then wash with water, and after all the acid is removed stain with logwood or picrocarmine. (i.) Also tease a piece in normal saline containing a trace of methyl-violet.

(c.) Silver one of the tendons to show the endothelium covering its surface (p. 166).

(7.) Place a fresh tendon in ammoniacal carmine (10-15 mins.), wash and place in very dilute Delafield's logwood (10-15 mins.). Wash, tease; and mount in balsam. The tendon cells are red, their nuclei blue, and the tendon fibres rosy.

4. Aponeurosis.-The best is the femoral.

(a.) Remove the membrane and stretch it on a slide by the "semi-desiccation method (p. 159), and after it is fixed to the slide apply a drop of acid methyl-green, or normal saline with methyl-violet. The nuclei are thereby stained, and the crests and ridges of the cells are made visible.

(b.) It may be fixed rapidly on a slide with absolute alcohol and stained with logwood. Or osmic acid may be used to fix it. (c.) Show the effect of acetic acid.

5. Areolar Tissue.-(a.) Dissect out some from the intermuscular septa of the leg muscles. Stain with methyl-violet in normal saline. This stains the cells. Or use acetic-fuchsin (p. 92).

6. Yellow Elastic Fibres. These are found in the septa between the lymph-sacs. Cut out a septum, fix it on a slide by "semidesiccation," and then add acetic acid. Or make another preparation and stain it with a weak solution of methyl-violet-5B (p. 93).

7. Pigment-Cells.-(a.) These are found in the web of the frog's foot. Stretch the web between the toes, harden it in absoluté alcohol for an hour or so, peel off the skin, and mount it in balsam (p. 173).

(b.) Or use the mesentery, or almost any blood-vessel; add dilute acetic acid and mount in glycerine.

8. Hyaline Cartilage.-(a.) Use either the episternum, scraping off the perichondrium, or make a section of the articular cartilage on the femur or tibia. Stain in hæmatoxylin. Or, before cutting,

the cartilage may be hardened for an hour in absolute alcohol.

(b.) A silver nitrate preparation may also be made (p. 151).

9. Endothelium of Mesentery.-Place pieces of mesentery in AgNO3 (.25 per cent.) for half an hour, wash in distilled water and expose to light in 50 per cent. alcohol.

Part may be afterwards stained in hæmatoxylin.

10. Endothelium of Great Lymph-Sac.-Open the abdomen from the front along the middle line, turn aside the intestines, and note the kidney. A.thin membrane or septum stretches from this to the abdominal wall. With a fine pipette filled with silver nitrate solution perforate this membrane and allow silver nitrate to flow into the great lymph-sac. Expose the membrane to light, and then examine in glycerine to see endothelium and stomata (p. 239). One-half may be stained with hæmatoxylin to show the nuclei. Or expose the septum from behind as directed at p. 238.

11. Adipose Tissue.-Use the yellow-coloured fat bodies found in the abdominal cavity.

(a.) Tease a piece in glycerine.

(b.) Use osmic acid (p. 169).

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