i8 



NA TURE 



May 5, 1892 



therefore made by Baudin, of Paris, some very sensitive mer- j 

 curial thermometers. The investigations made with the help of; 

 these instruments on the brain and blood temperatures bring to ' 

 light new evidences of activity in the nerve centres. There are 

 sometimes very extensive temperature developments under the 

 influence of special excitements quite independent of psychical 

 activity. The change in the nutrition of the nerve-cells, and 

 not their specific activity, seems to be the most important source 

 of heat in the brain. Thus Prof. Mosso would explain the 

 marked effect on brain temperature of ordinary irritants where 

 the increase is far higher upon the introduction of such than 

 upon any psychical work done by the brain. 



The following is an abstract of Prof. Mosso's Croonian 

 Lecture : — 



In his investigations on the temperature of the brain the author 



that of the blood in the arteries. This is due to the very great 

 radiation of heat which takes place from the surface of the 

 head. 



The brain when subjected to the action of the ordinary in- 

 terrupted current rises in temperature. The rise is observed 

 earlier in the brain than in the blood, and the increase is greater 

 in the brain than in the general blood-current or in the rectum. 

 During an epileptic seizure, brought on by electrical stimulation 

 of the cerebral cortex, the author observed within twelve minutes 

 a rise of l* C. in the temperature of the brain. 



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

 interior of the body ; 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 o°'2 or o°'3 C. above that of the interior of the body. 



Fig. I. — Dog rendered insensible with laudanum. The upper (thin) line represents the temperature of the interior of the body, the middle (thin 

 line the temperature of the blood in the carotid artery, the third (thick) line the temperature of the brain, a, injection of 3 c.c. laudanum ; 

 B, blast of a trumpet ; c, p, e, electric stimulation of the brain. The ordinate is marked in tenths of a degree Centigrade, the abscissa in 

 periods of ten minutes. 



has employed, in preference to the thermo-electric pile, exceed- 

 ingly sensitive mercurial thermometers, constructed specially for 

 the purpose. Since each thermometer contains only four grams 

 of mercury, the instruments respond very rapidly to changes of 

 temperature, and a change of not more than o'''<X)2 C. can 

 easily be measured by means of them. The author has studied 

 the temperature of the brain, comparing it with that of arterial 

 blood, of the muscles, and of the interior of the body. His obser- 

 vations were made on animals under the influence of morphia or 

 various anaesthetics, and also on man. 



The curves of the observations made show that in profound 

 sleep a noise, or other sensory stimulus, is sufficient to produce 

 a slight development of heat in the brain, without the animal 

 necessarily awakening. 



In profound sleep the temperature of the brain may fall below 



NO. 



75, VOL. 46] 



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 diff'erence of tem- 

 perature thus brought about is great and constant. In one in- 

 stance, the temperature of the brain was i°'6 C. above that of 

 the arterial blood in the aorta. Such observations warn us not 

 to regard the muscles as forming, par excellence, the thermo- 

 genic 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 interior of the body, the difference amounting to 

 o^'S oro°-6 C. 



