THE CONTROL OF RESPIRATION 91 



measured and the proportions of total heat lost by various 

 routes were established. In this way the activity of the effector 

 side of the control system could be rapidly and accurately 

 measured. Temperatures of the body were determined with 

 thermocouples in the rectum, skin, and in the head at several 

 places only an inch away from the hypothalamus. Continuous 

 measurements at these points showed marked differences be- 

 tween temperatures in the head and those of the rectum and skin. 

 The discrepancies existed during rest, after exercise, and follow- 

 ing eating of ice or hot fluids. It is clear, therefore, that the rectal 

 temperature does not give a good indication of the fluctua- 

 tions at the hypothalamic receptors. This observation is signifi- 

 cant because rectal temperatures had previously been used to 

 show the absence of a correlation between internal temperature 

 and the heat-regulating mechanisms. On this basis the role of 

 the hypothalamic receptors appeared to be a subsidiary one. In 

 the light of the temperature measurements in the region of the 

 hypothalamus itself, it was therefore necessary to repeat these 

 observations, using the hypothalamic conditions as an indicator 

 of the internal temperature. These experiments demonstrated 

 the marked correlation between temperature at the hypo- 

 thalamus and the output of the regulating mechanisms. This can 

 be seen in fig. 26 which shows the changes in head temperature 

 and skin temperatures, together with the heat loss through 

 evaporation and by vaso-dilatation of the skin. Ice was taken by 

 the subject at three points and a marked correlation is seen 

 between the fall in internal temperature and the heat lost by the 

 effector system. Another striking feature is that following the 

 consumption of ice the skin temperature showed a distinct rise 

 of about 0-6° C. Evidently the lowered internal body tempera- 

 ture affects the hypothalamic receptors which stimulate the 

 thermostat which decreases the evaporative heat loss by reduc- 

 ing the sweat-gland activity. The consequent drying of the skin 

 produced the rise in skin temperature. It appears that for these 

 heat-controlling responses the internal receptive mechanism 

 provides more adequate information to the thermostat about 

 heating conditions of the body than would a receptive mechan- 



