214 INFLUENCE OF THE BLOOD ON THE BRAIN. 



through the lungs does not undergo that process of 

 oxygenation which is essential to life ; and as it is 

 in this state unfit to excite or support the action of 

 the brain, the mental functions become impaired, 

 and death speedily closes the scene. If, on the 

 other hand, the blood be too highly oxygenated, as 

 by breathing oxygen gas instead of common air, the 

 brain is too much stimulated, and an intensity of ac- 

 tion, bordering on inflammation, takes place, which 

 also soon terminates in death. 



Such are the consequences of the two extremes ; 

 but the slighter variations in the state of the blood 

 have equally sure, although less palpable, effects. 

 If its vitality be impaired by breathing an atmo- 

 sphere so much vitiated as to be insufficient to pro- 

 duce the proper degree of oxygenation, the blood 

 then affords an imperfect stimulus to the brain ; and 

 as a necessary consequence, languor and inactivity 

 of the mental and nervous functions ensue, and a 

 tendency to headache, syncope, or hysteria makes 

 its appearance. This is seen every day in the list- 

 lessness and apathy prevalent in crowded and ill- 

 ventilated schools ; and in the headaches and liability 

 to fainting which are so sure to attack persons of a 

 delicate habit in the contaminated atmosphere of 

 crowded theatres, churches, and assemblies. It is 

 seen less strikingly, but more permanently, in the 

 irritable and sensitive condition of the inmates of 

 cotton-manufactories and public hospitals. In these 

 instances, the operation of the principle cannot be 

 disputed, for the languor and nervous debility con- 

 sequent on confinement in ill-ventilated apartments, 

 or in air vitiated by the breath of many people, are 

 neither more nor less than minor degrees of the 

 same process of poisoning to which I have formerly 

 alluded. It is not real debility which produces 

 them; for egress to the open air almost instantly 

 restores activity and vigour to both mind and body, 

 unless the exposure has been very long, in which 



