304 THE POPULAR SCIENCE MONTHLY. 



from which are given off" the various branches that distribute arterial 

 blood to every part of the brain-substance. After traversing this, the 

 blood returns by the Veins, greatly altered in its chemical composi- 

 tion ; especially as regards the loss of free oxygen, and its replace- 

 ment by various oxy-compounds of carbon, hydrogen, phosphorus, etc. 

 that have been formed by a process analogous to combustion. Now 

 if one, two, or three of the Arterial trunks be tied, the total supply of 

 blood to the Brain is diminished ; but, in virtue of the " Circle of Wil- 

 lis," no part is entirely deprived of blood ; and the functional activity 

 of the Brain is still maintained. If, however, the fourth artery is com- 

 pressed so as to prevent the passage of blood, there is an immediate 

 and complete suspension of activity ; the animal becoming as uncon- 

 scious as if it had been stunned by a severe blow, but recovering as 

 soon as the blood is again allowed to flow through the artery. In 

 fact, the "stunned" state produced by a blow on the head is not 

 directly dependent upon the effect of that blow on the Brain, which 

 may have sustained no perceptible injury whatever ; the state of in- 

 sensibility being due to the paralysis of the Heart and suspension of 

 the Circulation, induced by the " shock : " and the like paralysis with 

 the same result may be produced by a blow on the Epigastrium (act- 

 ing on the great "solar plexus "of nerves), or some overpowering 

 Mental emotion. Again, there is a curious affection termed Hysteric 

 Coma, which consists in the sudden supervention of complete insen- 

 sibility, and the equally sudden and complete return of conscious in- 

 telligence, without any other indication of Brain-disorder. The in- 

 sensibility may come on while the patient is talking, so as to interrupt 

 the utterance of a sentence ; and, the moment that it passes off, the 

 series of words is taken up and completed, without the patient being 

 aware that it has been interrupted. With our present improved 

 knowledge of the action of the " vaso-motor " system of Nerves in 

 producing local contractions of the Arteries, and of its liability to be 

 influenced by those Emotional irregularities in which Hysteria essen- 

 tially consists, we can scarcely doubt that this affection is due to a 

 temporary disturbance of the Circulation through that agency. Fur- 

 ther, if the Blood transmitted to the Brain, though not deficient in 

 quantity, be depraved in quality by the want of Oxygen and the ac- 

 cumulation of Carbonic acid (as happens in Asphyxia), there is a grad- 

 ually increasing torpor of the Mental Faculties, ending in complete 

 insensibility. 



Thus the dependence of Mental activity of even the most element- 

 ary kind, upon the Physical changes kept up by the circulation of 

 oxygenated Blood through the Brain, can be shown experientially to 

 be just as direct and immediate as is the dependence of the Electric 

 activity of a Galvanic battery upon the analogous changes taking 

 place between its Metals and its exciting Liquid. If we say that 

 Electricity is the product of Chemical change in the one case, I see 



