May 5, 1892] 



NATURE 



19 



Observations made while an animal is awake tend to show 

 that the development of heat due to cerebral metabolism 

 may be very considerable, 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 tempeiature ob- 

 served to follow, in the dog, upon great psychical activity was 

 not more than o'oi C, When an animal is conscious, no 



sensible by an anaesthetic, one no longer obtains a rise of 

 temperature upon stimulating 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 chemical 

 action. 



In another experiment, in an animal rendered insensible with 

 chloral, the curves of temperature show that when the muscles 

 of a limb are made to contract, the temperature of the muscles 

 rises, but falls rapidly as soon as the stimulation ceases, soon 

 returning to the normal. This is not the case, however, with 



Fig. 2.-Dog (female) rendered insenMble with chloroform and then with laudanum. The upper ine represents tl,e temperature "' '|^=. ''^f'"^' Jn 

 middle (Thicker) line that of the brain, the lower that of the arterial blood in .he carotid artery. Ja and M, psychical emotion; c, electric stimulation 

 of the brain ; d, injection of 14 c.c. laudanum (intravenous) ; e and i, electric stimulation of the brain. 



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 

 anaesthetics. He shows that these drugs suspend the chemical 

 functions of the nerve-cells. In a dog rendered completely in- 



the brain excited by an electric current. Here the stimulus 

 gives rise to a more lasting production of heat ; the temperature 

 may continue to increase for several minutes after the cessation 

 of the stimulation, indeed, often for half an hour. This may 

 possibly explain why, upon an electric stimulation of the 

 cerebral cortex, the epileptiform convulsions are not imme- 

 diately developed, but only appear after the lapse of a latent 

 period of several minutes. 



This experiment may be made to show the elective action 

 exercised upon the brain by stimulant remedies. The injection 

 of ID centigrams of cocaine hydrochlorate produces a rise of 



NO. II 75, VOL. 46] 



