THE SKIN. 201 



CHAPTER IV. 



Perspiration differs in various Temperatures. More in dry than in 

 moist Air Prepared in Glajids for the Purpose. Some Ani- 

 mals do not perspire jS Oily Excretions from the Skin. Tight 

 Clothing, Hats, &c., prevent Removal of these Excretions. 



477. This perspiration differs in various conditions of 

 the atmosphere. .Heat increases the activity of the cutane- 

 ous blood-vessels, and the perspiratory action, and also the 

 capacity of the air to receive vapor. ( 349, p. 152.) Evapo- 

 ration is therefore more rapid in warm than in cold weather. 

 A moving atmosphere brings to the body a constant suc- 

 cession of layers of dry air, which absorb the moisture more 

 rapidly. The perspiration is therefore mere free in a windy 

 than in a still day; and, if the wind is very dry and hot, 

 this evaporation is still further increased. The sirocco, 

 which comes over Sicily from the south, is so dry and hot as 

 to produce in the skin a parching and painful dry ness, and 

 sometimes excites disease. 



478. When the air is saturated or loaded with moisture, 

 the evaporation is checked, and the perspiration is not car- 

 ried off so freely ; and sometimes this interruption causes 

 a serious disturbance and burden to the system. The waste 

 that is carried off through the skin gives important relief to 

 the whole body, and, if this is interrupted, oppression follows, 

 and the frame is languid. In some of the sultry dog-days, 

 we are languid, because the atmosphere, being already filled 

 with vapor, does not carry off the watery exhalations of the 

 skin, and relieve the body. From this cause, internal dis- 

 eases prevail more in low and damp situations of warm 

 climates than in dry. On the banks of the southern and 

 western rivers, this is most painfully manifested. 



479. In this work of perspiration, the inner skin performs 

 all the active duty. It not only throws this fluid out, but it 

 originally forms it out of the elements which are found in 

 the blood. This work of formation is done in little glands 



