Page:First course in biology (IA firstcourseinbio00bailrich).pdf/478

 CHAPTER II

THE SKIN

—The experiments should be assigned in turn to the pupils as each chapter is reached: e.g. this set of 13 will leave 3 pupils in a class of 39 to stand responsible for each experiment. Each pupil should do the work separately and credit may be given for the best results. Encourage (or require) each pupil to try every experiment and record them in a note book.

Experiment 1. (At home or in class.) Albinism.—Study a white rabbit as an example of albinism. Does albinism affect only the skin? What evidence that its blood is of normal color?

Experiment 2. Use of Hairs on the Skin.—Let one pupil rest his hand upon the desk behind him while another touches a hair on his hand with a pencil. He should speak at the moment, if it is felt. Do the hairs increase the sensitiveness of the skin? What was their use with primitive man? Are the hands of all your acquaintances equally hairy? Are the hairs to be classed as rudimentary? Will they disappear? Will the race become baldheaded?

Experiment 3. (Home or school.) Invisible Perspiration.—Hold a piece of cold glass near the hand or place the cheek near a cold window pane and notice for evidence of moisture. Its source?

Experiment 4.—Effect of Evaporation on Temperature.—Read a thermometer and cover its bulb with a moist cloth. Read again after twenty minutes. Repeat experiment in breeze.

Experiment 5. Moisten one hand and allow it to dry. Touch the other hand with it. Explain result.

Experiment 6. Absorbing Power of Fabrics.—Wet the hands and dry them upon a piece of cotton cloth. Repeat with woolen, linen, and silk. Arrange in list according to readiness in absorbing water.

Experiment 7. Rates of Drying.—Immerse the cloths in water and hang them up to dry. Test their rates of drying with dry powder or by touch.

Experiment 8. Test Looseness of Weave of above cloths by measuring the distance pieces of equal length will stretch.

Experiment 9. Does Cotton or Wool protect better from Radiant Heat?—Lay a thermometer in the sun for ten minutes, first covering