84 Temperature of Brain and Psychical Activity. [Mar. 24, 



the author observed within twelve minutes a rise of 1° C. in the 

 temperature of the brain. 



As a rule the temperature of the brain is lower than that of the 

 rectum ; but intense psychical processes, or the action of exciting 

 chemical substances, may cause so much heat to be set free in the 

 brain that its temperature may remain for some time 0'2° or 0*3° C. 

 above that of the rectum. 



When a dog is placed under the influence of curare, the tem- 

 perature of the brain remains fairly high, while that of the muscles 

 and that of the blood falls. The difference of temperature thus 

 brought about is great and constant. In one instance, the temperature 

 of the brain was 16° C. above that of the arterial blood in the aorta. 

 Such observations warn us not to regard the muscles as forming, par 

 excellence, the thermogenic tissue of the body. 



In order to show how active are the chemical processes in the brain, 

 it is sufficient to keep the animal in a medium whose temperature is 

 the same as that of the blood. When the effects of radiation through 

 the skull are thus obviated, the temperature of the brain is always 

 higher than that of the rectum, the difference amounting to 0*5° or 

 0'6° C. 



Observations made while an animal is awake tend to show that the 

 development of heat due to cerebral metabolism may be very con- 

 siderable, even in the absence of all intense psychical activity. The 

 mere maintenance of consciousness belonging to the wakeful state 

 involves very considerable chemical action. 



The variations of temperature, however, observed in the brain, as 

 the result of attention, or of pain or other sensations, are exceedingly 

 small. The greatest rise of temperature observed to follow, in the 

 dog, upon great psychical activity was not more than 0*01° C. When 

 an animal is conscious, no change of consciousness, no psychical 

 activity, however brought about experimentally, produces more than 

 a slight effect on the temperature of the brain. 



The author shows an experiment by which it is seen that, as part 

 of the effect of opium, the brain is the first organ to fall in temperature, 

 and that it may continue to fall for the space of eighteen minutes, 

 while the blood and the vagina are still rising in temperature. 



The author discusses the elective action of narcotics and anaes- 

 thetics. He shows that these drugs suspend the chemical functions 

 of the nerve-cells. In a dog rendered completely insensible by an 

 anaesthetic, one no longer obtains a rise of temperature upon stimu- 

 lating the cerebral cortex with an electric current. These results 

 cannot be explained as merely due to the changes in the circulation of 

 the blood. The physical basis of psychical processes is probably of 

 the nature of chrmical action. 



In another experiment, in an animal rendered insensible with 



