230 THE HUMAN BODY. 



body; linen permits any change in the external tempera- 

 ture to act almost at once upon the skin. After an un- 

 avoidable exposure to cold or wet, the thing to be done is 

 of course to maintain the cutaneous circulation; movement 

 should be persisted in, and a thick dry outer covering put 

 on until warm and dry underclothing can be obtained. 



In healthy persons, a temporary exposure to cold, as 

 a plunge in a bath, is good, since in them the sudden con- 

 traction of the cutaneous arteries soon passes off, and is 

 succeeded by a dilatation causing a warm healthy glow on 

 the surface. If the bather remain too long in cold water, 

 however, this reaction passes off, and is succeeded by a more 

 persistent chilliness of the surface, which may last all day. 

 The bath should therefore be left before this occurs; but 

 no absolute time can be stated, as the reaction is more 

 marked and lasts longer in strong persons and in those used 

 to cold bathing than in others. 



Why does linen not form a good inner garment under such circum- 

 stances? What should be done after unavoidable exposure to cold 

 or wet? 



Why is a plunge in a cold bath useful to healthy persons? What 

 results if a person remains too long in cold water? When should a 

 cold bath be left? What persons may remain longest with safety in 

 a cold baih? 



APPENDIX TO CHAPTER XV. 



1. A frog may be used to illustrate the beat of the heart. Ana- 

 tomically a frog's heart differs in many respects from that of a mam- 

 mal, but the phenomena of systole and diastole are essentially the same. 



2. Etherize a frog as before described. Cut off its head. Check 

 bleeding and destroy its spinal cord by forcing a pointed wooden peg 

 along the spinal canal. 



3. Laying the animal on its back, carefully divide with scissors 

 the skin along the middle line of the ventral surface for its whole 

 length. Make cross cuts at each end of this longitudinal one and 

 pin out the flaps of skin. 



