NORMAL VARIATIONS IN TEMPERATURE. 429 



MEASUREMENT OF TEMPERATURE. 



On account of the slight degrees of variation that occur in 

 the temperature of man, all the changes 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 

 contact 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. 



I. The temperature of the body as a whole normally undergoes 

 certain variations, some of which are: (1) Regular and peri- 

 odical, depending upon the time of day, the ingestion of food, 

 and the age of the individual. (2) Accidental circumstances, 

 such as mental or bodily exertion. 



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

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

 variation, which normally does not much exceed 1 C., is much 

 exaggerated in hectic fever. 



6. The temperature rises after a hearty meal and falls during 





