426 MANUAL OF PHYSIOLOGY. 



(constant temperature), and to animals with temperatures varying 

 with their surroundings " Poikilothermic " (or changing tempera- 

 ture), instead of the words warm- and cold-blooded. 



MEASUREMENT OF TEMPERATURE. 



On account of the slight degrees of variation that occur in the 

 temperature of man, all the changes taking place can be measured 

 with a thermometer having a short scale of some 20 degrees, each 

 degree of which occupies considerable length on the instrument, 

 so that very slight variations may be easily appreciated. Such 

 thermometers, with an arrangement for self- registering the maxi- 

 mum height attained by the column of mercury, are in daily use 

 for clinical observation, for the temperature of the body is now a 

 most important aid to diagnosis and prognosis in a large class of 

 diseases. 



As heat is constantly being lost at the surface of the body, the 

 skin is colder than the deeper parts, and in order to avoid varia- 

 tions caused by this surface loss which depends in a measure on 

 the temperature of the air special arrangements are necessary 

 to prevent the thermometer being too much influenced by it. 

 The instrument may be brought into close proximity to the deeper 

 parts by being introduced into one of the mucous passages, where 

 it is surrounded by vascular tissue. In animals the rectum is the 

 most convenient part for the application of the thermometer, but 

 in clinical practice it is usually placed under the tongue, or in 

 the arm-pit, the bulb being held so that on all sides it is in con- 

 tact with the skin and protected from the cool air. 



The variations at different parts of the body are but slight, and 

 the average normal temperature in man is found to be about 37 C. 



NORMAL VARIATIONS IN TEMPERATURE. 



The normal temperature undergoes certain variations, some of 

 which are : (1.) Regular and periodical, depending upon the time 

 of day, the rngestion of food, and the age of the individual. (2.) 

 Accidental circumstances, such as mental or bodily exertion. 



fi. The temperature is highest between 4 and 5 P.M. and lowest 

 between 2 and 4 A.M., the transition being gradual. This diurnal 



