430 TEXT-BOOK OF PHYSIOLOGY. 



may be obtained by the introduction of a thermometer into the mouth, 

 the rectum, the vagina, or the axilla. As a result of many observa- 

 tions it has been found that the temperature of the rectum is, on 

 the average, 37.2 C.; that the mouth, 36.8 C.; that of the axilla, 36.9 C. 

 Owing to radiation and conduction, the surface temperature is 

 lower than that of either the mouth or rectum, and varies to a slight extent 

 in different regions of the body: e.g., at a room-temperature of 20 C. 

 the skin of the pectoral region has a temperature of 34.7; that of the 

 cheek, 34.4; that of the calf, 33.6; that of the tip of the ear, only 

 28.8, etc. 



In the interior of the body, especially in organs in which oxidation takes 

 place rapidly, and which at the same time are protected by their anatomic 

 surroundings from rapid radiation, the temperature is higher than that 

 observed in the rectum. From an investigation of the temperature of the 

 blood as it emerges from the liver, the muscles, the brain, alimentary canal, 

 etc., it is evident that these organs have a higher temperature than the 

 rectum. 



As the chemic changes underlying physiologic activity vary in intensity 

 and extent in different regions of the body, there would be marked varia- 

 tions in their temperature were it not that the blood, having a large ca- 

 pacity for heat-absorption, distributes the heat almost uniformly to all por- 

 tions of the body, so that at a short distance beneath the surface the tem- 

 perature varies but a few degrees. 



In the dog the temperature of the- blood in the aorta and in its principal 

 branches is approximately 38.3 C. In passing through the systemic cap- 

 illaries the temperature falls from radiation and conduction to surface 

 temperature, to again rise as the venous blood approaches the deeper regions 

 of the body. In the neighborhood of the renal veins and in the superior 

 vena cava, the temperature is again that of the aorta. In the portal vein 

 the temperature rises to 40.2 C.; in the hepatic vein, to 40.6 C. In the 

 right ventricle, owing to the admixture of blood from different localities 

 having different temperatures, the temperature falls to 38.2 or 40.4. In 

 passing through the pulmonary capillaries the temperature of the blood 

 again falls, so that in the left ventricle it will register from 38 C. to 40.2 C. 

 There is thus usually a difference between the two sides of the heart of about 



0.2 C. 



Variations in the Mean Temperature. The mean temperature of 

 the human body for twenty-four hours, which for the mouth and the rectum 

 may be accepted at 36.8 C. and 37.2 C. respectively, is subject to variations 

 from a variety of circumstances, such as age, periods of the day, food, exer- 

 cise, etc. 



Age. At birth the temperature of the infant is slightly higher than 

 that of the mother, registering in the rectum about 37.5 C. In a few hours 

 it rapidly declines to about 36.5, to be followed in the course of twenty-four 

 hours by a rise to the normal or slightly beyond. During childhood the 

 temperature gradually approximates that of the adult. In old age the tem- 

 perature rises, as a rule, and attains a maximum at eighty years of 37.4 C. 



Periods of the Day. The observations of Jiirgensen show that there is 

 a diurnal variation in the mean temperature of from 0.5 C. to 1.5 C., the 



