238 CRILE-FRICKE— APPLICATION OF BIOPHYSICAL 



swers have not been directly determined for most organs. In the 

 case of a muscle at work, A. V. Hill^ has found that there is a 

 maximum efficiency of fifty per cent. From an estimation of the 

 work done by the organs it is safe to assume that for most organs 

 the major portion of the chemical energy obtained through the oxy- 

 gen consumption is directly transformed into heat. The chemical 

 energy of the oxygen consumed by an organ under excitation corre- 

 sponds to a temperature increase of a few tenths of a degree Centi- 

 grade per minute. The magnitude of this change indicates the 

 feasibilit}^ of employing thermocouples for the temperature measure- 

 ments in the study of metabolic processes. 



In the studies reported here our attention has been directed espe- 

 cially to the measurement of the temperature changes which occur 

 in the brain. As compared with most other organs, the oxygen con- 

 sumption of the brain is large. It seems probable that the energy 

 corresponding to this consumption is not directly converted into heat 

 for the sole purpose of maintaining the brain temperature, but that 

 it is primarily used by the brain in its special activities, finally ap- 

 pearing as heat in the brain or in other parts of the body. If this is 

 so we would expect that activation of the brain would be accompanied 

 by temperature changes large enough to be recorded. 



It is evident, however, that changes in the circulation of the blood, 

 due to vaso-constriction and vaso-dilation in the different parts of the 

 body, must be an important factor in the production of the tempera- 

 ture changes in an organ. This fact makes the interpretation of the 

 records of temperature change quite complicated. 



Experimental Technique. — The temperature changes in the 

 organs studied were measured by means of copper-constantan ther- 

 mocouples combined with mirror galvanometers. The time of vibra- 

 tion of the galvanometers was about seven seconds. The galvanom- 

 eter deflections were reflected on a common scale, the resistances 

 in each circuit being so adjusted that a deflection of one division on 

 the scale (equal to two millimeters) corresponded to a temperature 

 change of one one-hundredth of a degree Centigrade. The scale 

 covered a temperature range of 6° C. A specially designed poten- 

 tiometer made possible the immediate introduction into each thermo- 



8 Hill, A. v., Jour. Physiol., 1913. XLVL, 435- 



