Page:First course in biology (IA firstcourseinbio00bailrich).pdf/481

 it with a woolen cloth. Note change in reading. After it regains first reading, repeat, covering it with a cotton cloth of same weight and texture? Conclusion? Expose wrists or arms to sun for five minutes, one protected by the cotton, the other by the wool. Result? Conclusion?

Experiment 10. Rates of Heat Absorption and Radiation by Different Colors.—Expose thermometer to sunlight, covered successively by pieces of cloth of same thickness, material, and texture. Use black, blue, red, yellow, and white cloth. Note rise of temperature for equal times in each case; also the fall of temperature for equal times after removal to shade.

Experiment 11. Effects of Dry Powders.—Prepare two squares from the same piece of leather (e.g. an old shoe). Moisten them both, and apply face powder to one. Which dries more quickly? Repeat after oiling them. Powder a portion of the face or arm daily for a week and compare with the clean portion.

Experiment 12. Dissect the kidney of an ox or sheep, making out the parts mentioned in the text, p. 26.

Experiment 13. (In class.) Emergency Drill.—Have one pupil wet an imaginary burn on the arm of another, treat it with flour or soda, and bandage. (See text.)

The Skin has Two Layers.—The outer layer is called the epidermis; it is thinner, more transparent, and less elastic than the inner layer, or dermis. The epidermis is composed of epithelial cells packed close together (see colored Fig. 1).

The dermis, or inner layer, is a closely woven sheet of connective tissue (colored Fig. 1) containing a great number of sweat and oil glands, roots of hairs, blood vessels, absorbent vessels (lymphatics), and nerves (colored Fig. 1). The dermis is sometimes called the true skin because it is of greater importance than the epidermis. It is united loosely to the underlying organs by a layer of connective tissue. It is in this layer that fat is stored. The upper surface of the dermis rises into a multitude of projections (see colored Fig. 1) called papil'læ (singular, papilla). The epidermis fits closely over them and completely levels up the spaces between them except on the palms and the soles. Here the papillæ are in rows, and there is a fine