THE MAINTENANCE OF THE BODY TEMPERATURE 197 



98.6 F. (In all the following discussion the familiar 

 Fahrenheit system will be used.) The standard just 

 quoted is for the mouth. The body temperature is often 

 estimated by placing the thermometer elsewhere, as in the 

 armpit or the rectum. The rectal temperature is the most 

 reliable, and is usually higher by half a degree, or a little 

 more, than that of the mouth. It is clear that the tem- 

 perature of the skin cannot be a constant one ; it is affected 

 both by the external conditions and by the variations 

 of blood-flow in the superficial vessels. 



There are small but distinct changes of body tempera- 

 ture during each day. The lowest figures are noted early 

 in the morning before one has become active and when the 

 sense of prostration is apt to be overpowering. A gentle 

 upgrade is maintained until the maximum is reached in the 

 late afternoon or early evening. The average extent of the 

 rise is about 1 F. It coincides suggestively with the 

 temperamental change, which is to be observed from a 

 prosaic and literal frame of mind to a condition of emotional 

 instability. Compared with the morning, the evening is 

 a feverish period. When there is actual fever the diurnal 

 ascent of the temperature often adds considerably to the 

 restlessness and discomfort of the patient as night ap- 

 proaches. 



After we have made allowance for such irregularities it 

 remains true that the approximate constancy of the tem- 

 perature is one of the most wonderful facts which the 

 physiologist has to explain. Uniformity of temperature 

 implies equality of heat production and heat loss. Our 

 task, then, is to show how this equality is continued in the 

 face of variable factors tending to disturb it. Artificial 

 contrivances for keeping constant temperatures in cer- 

 tain chambers may be considered with advantage before we 

 attempt to analyze a mechanism so much more intricate 

 than they. There are two principles on which incubators 

 or thermostats may be operated: (1) The heat given to the 

 system may be increased or diminished to keep pace 

 with the heat lost; (2) a constant supply of heat may be 



