2d. Hold the apparently dry hand near a looking-glass, and the invisible vapor will soon be condensed, and cover the glass with a slight dew. 656. It is important that this excretion be maintained with steadiness and regularity. When the action of the perspiratory glands is suppressed, all the vessels of the different organs will suffer materially, and become diseased, by the redundant waste matter that should be carried from the system. If a person is vigorous, the action of the organs, whose functions are similar to those of the skin, as channels for the exit of waste matter, will be increased, and thus relieve the diseased state of the body. But the over-taxing of these organs, to relieve the system, often produces a diseased action in themselves. -=-=-=-=-=-=-=-=-=-=-=-= What were his conclusions? 655. What is the average amount of perspiration every twenty-four hours? What is insensible perspiration? What is sensible perspiration? How can the existence of the excretion of the skin be shown? Give the 2d experiment. 656. Why is it important that these excretions be maintained regularly? -=-=-=-=-=-=-=-=-=-=-=-= [Illustration: Fig. 117. 1, 1, The lines, or ridges of the cuticle, cut perpendicularly. 2, 2, 2, 2, 2, The furrows, or wrinkles of the same. 3, The cuticle. 4, 4, 4, The colored layer of the cuticle. 5, 5, The cutis vera. 6, 6, 6, 6, 6, The papillæ. 7, 7, Small furrows between the papillæ. 8, 8, 8, 8, The deeper furrows between each couple of the papillæ. 9, 9, Cells filled with fat. 10, 10, 10, The adipose layer, with numerous fat vesicles. 11, 11, 11, Cellular fibres of the adipose tissue. 12, Two hairs. 13, A perspiratory gland, with its spiral duct. 14, Another perspiratory gland, with a duct less spiral. 15, 15, Oil-glands with ducts opening into the sheath of the hair, (12.)] _Note._--Let the pupil review the anatomy and physiology of the skin from Fig. 117 or from anatomical outline plate No. 9. CHAPTER XXXIII. HYGIENE OF THE SKIN. 657. The sensibility of the skin, and the activity of the oil and perspiratory glands, are modified by the condition of the cuticle, the temperature of the skin and body, the purity and warmth of the air, and the character of the light to which the body is exposed. Thus, to maintain a healthy action of every part of this membrane, attention should be given to _Clothing_, _Bathing_, _Light_, and _Air_. 658. CLOTHING, in itself, does not bestow heat, but is chiefly useful in preventing the escape of heat from the body, and in defending it from the temperature of the atmosphere. In selecting and applying clothing to our persons, the following suggestions should be observed. 659. _The material for clothing should be a bad conductor of heat_; that is, it should have little tendency to conduct or remove heat from the body. This depends mainly on the property possessed by the material in retaining atmospheric air in its meshes.