COLD AND HEAT 499 



traction and subsequent dilatation of the peripheral blood vessels, with 

 consequent cooling of the blood and increased radiation of heat from the 

 surface. In most hydriatic methods for reducing temperature in fever, 

 friction of the skin should be the sine qua non, as otherwise the physical 

 cooling of the body is confined entirely to the periphery, the contraction 

 of the surface vessels driving the blood inward to the vital organs. The 

 superficial muscles then act as non-conductors, and heat production being 

 stimulated reflexly by the cold, an actual increase of internal temperature 

 may obtain. 



It is only by securing dilatation of the superficial vessels by friction 

 that the result first described can be prevented, for after the first shock 

 the peripheral vessels dilate, an increased supply of blood is brought to 

 the surface, is rapidly cooled and courses inward, only to be replaced by 

 more over-heated blood. The internal temperature is thus lowered, and 

 instead of an internal congestion being brought about, as may happen 

 when the skin is simply exposed to cold, we have a constant withdrawal 

 of heated blood from the interior. In this perpetual interchange not only 

 does cooling of the blood and body occur, but tha circulation is equalized 

 and congestions are overcome. 



The Sheet Bath. — Whole baths are impracticable for our larger 

 patients, and the sheet bath may be substituted to advantage for anti- 

 pyretic and other purposes to which the cold bath is adapted. A cloth 

 soaked in cold water, or ice poultice, is placed on the poll to prevent 

 determination of blood to the head, and a linen sheet, wet in water, of 

 from 50° to 80° F., is placed over the ani^pal, the surface being rubbed, 

 while dashing on the sheet water at the temperature of 50° to 60° F. 

 This process is continued for fifteen or twenty minutes, unless rigor is 

 induced. The method is valuable in the treatment of fever and insola- 

 tion. The general rationale is the same as in the case of ablutions, but 

 the antipyretic effect is more marked and permanent. The sheet may 

 be covered, while wet, by blankets, and converted into a wet pack. 



The Wet Pack is applicaible for general or local use, and for various 

 purposes. A linen sheet is dipped in water at a temperature of 50° to 

 70° F., and wrung out very thoroughly. A cold application is put on 

 the head and the sheet applied and covered with dry woolen blankets. 

 The duration of application is from one quarter to three hours, according 

 to the object in view. If it is used as a strictly antipyretic measure, it 

 should be changed frequently. The wet pack differs materially from 

 other hydriatic procedures in that reaction occurs slowly, for there is no 

 artificial stimulus in the shape of friction to accelerate it. The primary 

 contraction of the vessels is succeeded by partial dilatation of them, when 

 the blood from the interior of the over-heated body is cooled on the sur- 

 face by contact with the sheet and by vaporization of the water. Vascu- 

 lar contraction again occurs owing to the cooling, forcing the chilled 

 blood inward. So there is continual interchange of cooled and heated 

 blood, until the wet sheet has become thoroughly warmed. After the wet 

 pack is removed, the skin should be dried and the patient well blanketed. 



The interchange of blood is useful in relieving congestion of the 

 internal organs, in aiding 'nutrition by bringing to the periphery nutri- 



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