tissue, with numerous elastic fibres; the latter can be traced into, and become continuous with, the elastic fibres of the matrix (fig. 117, e, f). The matrix consists of fine branched and anastomosing fibres of elastic tissue, stained yellow with picric acid. Where the fibres are cut transversely, they appear as yellow dots or granules.

In addition to these, however, there are numerous granules of elastin scattered in the matrix. In this meshwork notice the nucleated cells stained red. Each cell has a capsule, but near the perichondrium they are smaller and flattened (i), while in the substance of the cartilage they are larger, oval, or spherical (r).

5. Acid Fuchsin Method.-Stain a section with a watery solution of acid fuchsin. Wash the section for a long time in absolute alcohol and mount in balsam. The network is intensely red, and the other parts uncoloured.

6. Double Staining of the Epiglottis. (i.) Stain a section with picro-carmine, and then faintly with logwood. Mount in balsam. To preserve the yellow colour of the fibrils, the clove-oil, with which the section is cleared up, must be made yellowish by dissolving in it a little picric acid. The fibres are yellow, f the cells red, and the nuclei purplish.

e.

(ii.) Stain another section with Fat-cells in perichondrium, c; dilute eosin-hæmatoxylin, and mount Elastic fibres; i. Superficial layers of it in Farrant's solution or balsam. smaller cells; r. Layer of larger cells with elastic granules, .;f. The cells take the logwood tint, and Perichondrium. Alcohol and picro- the fibres the colour of eosin.

carmine.

7. Ear of Pig or Horse.-Stain

a section in picro-carmine, and mount it in Farrant's solution. (L and H) Observe the skin, its glands and muscles. Neglect these, and note the perichondrium enclosing the cartilage with a characteristic arrangement of the cells. The cells near the surface are small, flattened, and parallel to it, while those in the centre are larger and arranged across the long axis of the section.

Between the cells is a matrix, which may be partly hyaline and partly yellow fibrous.

8. Transition of Hyaline to Elastic Cartilage (H).-Dissect out the arytenoid cartilage of an ox or sheep. Harden and preserve it in alcohol. Cut sections through the part where the hyaline cartilage merges into the elastic variety. This is quite visible to the naked eye, the elastic part being more opaque and yellowish white in tint. Stain a section with picro-carmine, and

mount it in Farrant's solution. On making a section of such a cartilage in the fresh condition, one part has the pale-bluish colour of hyaline cartilage, and the other part is very faintly yellow.

(a.) At one part observe hyaline cartilage, whose matrix gradually becomes fibrous. At first only a few scattered granules of elastin are seen, then the hyaline matrix is traversed by elastic fibres, and gradually the matrix loses its hyaline character, and becomes distinctly fibrous. Around each cell there is a clear area -hyaline-devoid of fibres (fig. 119).

LESSON X.

CONNECTIVE TISSUE.

THE group of Connective Tissues includes cartilage, ordinary connective tissue (with adipose tissue), adenoid or retiform tissue, mucous tissue, bone and dentine. (1) These all subserve more or less mechanical functions in the organism; (2) they all have much in common in structure, i.e., they are composed of cells, and an intercellular matrix, but usually the development of the matrix exceeds that of the cells, and (3) they are all developed from the mesoblast of the embryo.

ORDINARY CONNECTIVE TISSUE.

It consists of the following structural elements :

Corpuscles.

Fixed.

Migratory.

1. Flattened or lamellar cells, called also fixed con-
nective-tissue corpuscles.

2. Granular cells (eosinophilous cells?).
3. Vacuolated or plasma cells of Waldeyer.
Clasmatocytes of Ranvier (?).
Wandering cells or leucocytes.

B. Arrangement of these Elements.

(a.) Areolar, e.g., subcutaneous and submucous tissues.

(b.) Bundles in parallel groups, e.g., tendon (with parallel fibres) and fascia (fibres crossing at right angles).

(c.) Fenestrated fibrous membranes, c.g., omentum.

(d.) Compact bundles crossing in all directions, c.g., skin.

The lamellar cells are flattened or winged plates which lie on the bundles of fibrils. They have a large oval nucleus lying in a clear plate.

The granular cells, or "Mastzellen" of Ehrlich, are often found near blood-vessels, and in the fat present in areolar tissue, in the submucous tissue of the intestine, and in Glisson's capsule. The cells are often spherical, and the granules are numerous and proteid in nature, and stain with aniline dyes, e.g., eosin, hence the term sometimes applied to them "eosinophilous cells."

The plasma cells were formerly confused with the foregoing,

but in the plasma cells the protoplasm is vacuolated, and the vacuoles contain fluid. They sometimes have short processes. What the relation of the clasmatocytes to these other cells may be is so far not determined; nor, indeed, do we know the relation between the granular and the plasma cells.

The migratory cells are identical with the white blood-corpuscles or lymph-corpuscles, and may therefore be regarded as an adventitious element.

Yellow or Elastic Fibres occur in the ligamentum nuchæ of animals (large fibres); lig. subflava; stylo-hyoid ligament; connective tissue generally; in the walls of the air-tubes and lungs; the larger blood-vessels, especially arteries; the vocal cords and some ligaments of the larynx; many organs, e.g., spleen.

1. Yellow or Elastic Fibros-Thick Fibres (H).-Tease out in water a fragment of the ligamentum nucha of an ox; cover and examine it. It can be mounted in Farrant's solution.

(a.) Observe the broad

fibres with a definite outline, yellow in colour, refracting the light strongly, branching and anastomosing, and sometimes curling at their ends where they are broken across (fig. 120, f). A small quantity of white fibrous tissue will be found between and supporting the fibres (b).

(b.) Measure the size of one of the larger fibres. They are about 7-8 (10th inch) in diameter.

acid.

b

FIG. 120. f. Elastic fibres from the ligamentum nucha; b. Fine white fibrous tissue, X 300.

(c.) Irrigate with acetic The fibres are not affected, and no nuclei are revealed in them. They consist of the substance elastin, which is unaffected by acetic acid.

Make longitudinal and transverse sections of the ligamentum nuchæ (hardened in alcohol). Stain both in picro-carmine and mount in Farrant's solution. The connective tissue is thereby stained red, and the elastic fibres yellow.

2. L. S. Ligamentum Nuchæ (H).-Observe the fibres (yellowish), with a small amount of connective tissue (red) between them. The

fibres are broad with well-defined margins, have a feeble yellow tint, and are transparent. They branch and anastomose, and where ruptured curl up at their ends.

3. T.S. Ligamentum Nuchæ of Ox (H).-Observe the polygonal ends of the broad fibres-yellow--and nearly as broad as, or broader

than, a coloured blood-corpuscle, sometimes single, mostly in groups of three or more (fig. 121, a)-homogeneous throughout. A small amount of connective tissue (c) (red) between the groups.

4. Another section may be stained with a watery solution of magenta and mounted in Farrant's solution. The fibres are stained FIG. 121.-T.S. Ligamentum red, but the pigment is apt to diffuse into

fibres; c. Connective-tissue the Farrant's solution.
between them; n Nuclei
of connective-tissue

cor

5. A good plan is after hardening the puscles. Alcohol and borax- ligamentum nuchæ in alcohol to stain it in carmine, X 300. borax-carmine for several days, with the precautions stated at p. 65. Transverse sections show the white fibrous tissue between the elastic fibres, with its nuclei stained red (fig. 121, n)

6. Fine Yellow Elastic Fibres (H).-Harden the mesocolon or mesentery of a young rabbit in Flemming's fluid, and stain it in

FIG. 122.-Fine Network of

Elastic Fibres from the

Mesocolon of Rabbit.

Flemming's fluid and safranin.

methyl-violet as directed under Lesson X. 14, or stain it with magenta, when the elastic fibres are stained red; or with safranin after hardening in chromic acid.

1

(a.) Observe the network of fine elastic fibres. Many of the fibres have a diameter equal to one-sixth, or less, of that of a coloured blood-corpuscle (1 μ or 25.000 inch in diameter). The fibres branch and anastomose, and by carefully focussing, one can observe that the fibres do not all lie in

the same plane (fig. 122).

7. Fenestrated Membranes (H). Sometimes the elastin is so arranged as to form sheets or plates of elastic tissue, e.g., in the large arteries; at other times these are perforated with holes, and are called fenestrated elastic membranes.

With a pair of forceps tear off a little of the endocardium from a sheep's heart, spread it on a slide, and treat it with caustic potash. Or use the basilar artery, slit it up and scrape away the outer coats, and use caustic potash as before.

(a.) Observe near the margin of the preparation the elastic membrane with holes in it (tig. 123).