I ONI ROL OP BOD1 l l MP] R \ [M BK AND PEVFJJ 717 



magnitude of the change in cutaneous circulation i^ nevertheless depend- 

 enl ii])(ni the extenl of the area of the body thai is opposed to the change 

 in temperature, as seen in tin- dilatation of the skin vessels prior * 

 rise in body temperature wh6n a person is immersed in a warm bath. 



Although afferenl impulses from the skin are then eat im 



portance in adjusting the cutaneous blood supply according to the 



amounl of surface < ling thai has to occur, s further e also ; 



duced on them by the action on the nerve centers of temperatun 

 ferences in the blood itself. Thus, when the temperature of blood going 

 to the brain is raised by placing the carotid arteries on some heati - 

 vice or when the region of the corpora .striata is directly warmed, the 



skin vessels 1 ome dilated as if the animal had I o exposed I - eral 



warmth. 



When the loss of heal by radiation and conduction is no longer ade 

 quate to prevenl a rise in body temperature, or when the process 

 not operate on account of a high temperature in the environment, th< 

 '"-v of heal from the skin is mainly dependent upon tJn evajn 

 sweat. Under ordinary conditions this evaporation takes place at such 

 a rate that there is no visible perspiration on the surface of the body — 

 the so-called insensible perspiration. When the heal loss by this channel 

 must become greater, the perspiration is produced in larger amount, 

 thai it collects on the surface of the body; and. provided the conditions 

 the environment are such that evaporation can readily take p low- 



relative humidity . the amount of cooling of the body that can I 

 becomes very great. A man may exist without any marked rise in b< 

 temperature in a very hoi environment even when he is exposed to an 

 side temperature that is the same as thai of 1 y, or even greater. To 



encourage evaporation, however, he should be naked or very lightly clad, 

 and the air should be kepi in constant motion so that the la\ ait- 



next to the skin, which ordinarily very quickly become saturated \ 



vapor, are transferred and repla I by dryer air. Movement of the air 



also increases the heat loss by conduction, provided the temperature 

 the air is nol too near that of the body. 



The importance of the movemenl of air in the regulation I -- 



has been' clearly demonstrated by Leonard Hill. ' P. S Lee, and ol s who 

 have found that a greal part of the discomf ied by living 



stagnant air can be obviated by putting the air in motion by electri 

 without doing anything to improve its chemical purity. In one fam 

 leriment a number <>f young men were placed in an air-tight cabi 

 at the ordinary temperature of the room. Afl 



exhibit the symptoms usually attributed to polluted air; they became 

 drowsy and some of them developed headaches, \ small e 



