1892.] on Emotional Expression* ' 659 



in different regions of the brain, and they undergo wasting and 

 degeneration in chronic insanity. ^ 



What the changes in the protoplasm of the cerebral cells corre- 

 sponding with psychical activity really are we do not know, but, 

 thanks to the recent researches of Professor Mosso, of Turin, we 

 have now positive evidence that certain chemical changes, with 

 loss of heat, accompany their activity. Discarding the thermopile, 

 Professor Mosso has employed thermometers of extreme delicacy, and 

 by the application of these to the surfiice of the hemispheres has 

 found that the temperature of the brain — which in deep sleep falls 

 below that of the arterial blood — is raised even during the conti- 

 nuance of sleep by a noise or any sensory impression which infringes 

 upon the brain without causing awakening, or by the direct appli- 

 cation of the interrupted current to the cortex, and is raised very 

 decisively by the transition from the sleeping to the waking con- 

 dition. Professor Mosso has found that the brain of an animal 

 awake is hotter than that of an animal asleep, and that during con- 

 sciousness the temperature of the brain rises as much as • 5° C. above 

 that of the arterial blood, a clear indication that the maintenance of 

 consciousness involves chemical action. Strange to say. Professor 

 Mosso has not found that variations in conscious activity are accom- 

 panied by variations in the temperature of the brain. Once the tem- 

 perature corresponding with conscious activity has been attained it 

 remains, according to his experiments, steady, and is uninfluenced by 

 such psychical stimulation as he has been able to induce. But, for a 

 great variety of reasons, I cannot believe that there is any dead level 

 of consciousness or uniform distribution of functional activity in the 

 brain, and I am inclined to believe that Professor Mosso's conclusions 

 on this point will be modified by further experiments ; and especially 

 by simultaneous thermometric observations in different regions of the 

 brain during emotional disturbances of different kinds. AH analogy 

 and many recorded facts warrant the belief that, even if the hemi- 

 spheres have a function common to the mass of their grey matter, as 

 far as thought is concerned, there are during consciousness incessant 

 variations in the functional activity of different brain areas, and there 

 must be chemical changes, delicate but probably cognisable, corre- 

 sponding with these. 



An image, in matters scientific that are obscure and difficult to 

 comprehend, is sometimes obstructive and misleading, but it is some- 

 times useful, and in connection with the functional activity of the 

 brain I would suggest an image drawn from the phenomena of the 

 Polar lights as seen in our northern^sky. Think of the brain during 

 unconsciousness steeped in slumber, and imagine it to be the dark seg- 

 ment which forms the core of the aurora, which can sometimes be seen 

 before any luminosity has appeared. Think of the brain, again, as 

 it has passed from the sleeping to the waking condition, and is in 

 common conscious life, and conceive of it as spanned by the luminous 

 arch in constant motion, now rising, now falling, forming a continuous 



