DERMOTD SYSTEM. 293 



Action of Different Bodies on the Dermoid Texture, 



Q. What effect has light on the dermoid texture? 

 A. It whitens it, and this independently of heat. A 

 proof of this is, that clothing which does not exclude the 

 influence of heat from the skin, prevents the blanching of 

 the skin which light occasions. 



Q. What are the effects of heat on the dermoid tissue ? 

 *#. The first effect is to expand the texture and increase 

 the flow of fluids to and through it. In a higher degree, 

 heat produces redness, a kind of erysipelas. Applied more 

 powerfully, it reddens and vesicates the skin. In greater 

 intensity it produces the horny hardening, and lastly, it is 

 blackened and reduced to carbon. 



Q. In the production of redness and vesication, on 

 what does heat act? 



#. On the vital forces of the part; but the subsequent 

 steps are on the textural properties, and take place alike 

 in the dead and living skin. 



Q. Does the skin preserve an equality of texture? 

 /?. It does. It prevents the effects of a greatly in- 

 creased heat, refusing admission to the caloric; while in 

 very cold countries, it prevents the rapid escape of animal 

 internal heat. It is a curious fact, that internal organs ex- 

 posed to the air do not thus resist the changes of tempera- 

 ture. 



Q. How does cold affect the dermoid texture? 

 #. Variously, according to the degree at which it is 

 applied. First it contracts the vessels so that the usually 

 passing fluids cannot escape; the next degree produces 

 dermoid redness; and lastly, it brings on gangrene. 



