THERMAL PHENOMENA OF THE BODY 193 



7. Measurement of the body temperature. The great equal- 

 izer of the body temperature is the blood. Blood which has 

 flowed through the skin comes away cooled ; that which 

 comes from an organ like the liver or a working muscle, in 

 which active oxidations or other chemical changes have taken 

 place, is heated. In the great veins and in the heart the 

 warmer blood is mixed with the cooler, and an average 

 temperature of the arterial blood results. It is this average 

 temperature of the arterial blood flowing to the organs that 

 is approximately constant. 



When this blood flows for a time through an organ which 

 is itself not producing heat and is at the same time protected 

 from loss of heat, the organ ultimately takes on the tempera- 

 ture of the blood; so that by measuring the temperature of 

 such an organ we get the temperature of the blood itself. 

 It is customary to take the temperature in the mouth, the 

 bulb of the thermometer being placed under the tongue and 

 the lips kept closed. Subject to the variations mentioned 

 above, the temperature of the mouth is 98.6 F. 



8. The feeling of cold or warmth not a true test of the 

 body temperature. It is well at this point to warn the stu- 

 dent against confusing the body temperature with sensations 

 of cold or warmth. Just as visual sensations are aroused 

 only by that light which falls upon the sense organ espe- 

 cially adapted to respond to its stimulation, namely the eye, 

 while light falling upon the skin arouses no such sensation, 

 so heat and cold can excite the corresponding sensations 

 only when they act on special end organs adapted to receive 

 these stimuli, and these end organs are found only in the 

 skin, the mouth, and perhaps the nose, pharynx, and upper 

 oesophagus. We are therefore conscious only of the tempera- 

 ture of these organs ; we are not and cannot be conscious of 

 the temperature of the blood or of internal organs generally. 

 It is therefore clear that our feelings give us no reliable in- 

 formation as to the temperature of the internal parts of the 



