412 ACTION OF PROTOXIDE OF NITEOGEN. 



Emergence of of sleep, and in the article of death, but may, in a temporary 

 old impressions manner fog established by resorting to certain physical 



by artificial <* o ^ r J 



means. agents and drugs. Pressure upon the brain, either accident- 



ally or purposely applied, is well known to produce such a result, and, 

 in like manner, the inhalation of various agents, such as pure hydrogen 

 gas, the vapor of ether or chloroform, or other non-supporters of respira- 

 tion. On breathing these substances, anaesthesia is soon induced ; the 

 external world disappears ; and, on carrying forward the operation to a 

 due extent, the mind and the brain are literally left to themselves. Opium 

 acts in like manner, more particularly in the case of those who have ac- 

 customed themselves to its undue use. It, however, not only blunts 

 the force of new impressions, but exerts a positive agency in intensifying 

 the decaying, remains of old ones. Under its full influence, the true re- 

 lations of space and of time disappear : a century of events is lived 

 through in a single night ; the vision can comprehend distances ap- 

 proaching to the infinite ; and yet, under these circumstances, the mind 

 does not perceive a riot of incongruous combinations, but every thing is 

 presented in a methodical and orderly way pictures, all the parts of 

 which are in just proportions and severe keeping to each other, and long 

 sequences of events which maintain a mutual harmony. 



But, as I have just remarked, the equalization of new sensations with 

 Artificially in- old impressions, which is necessary for phantom appearances, 

 creased func- an( j fa Q incarnation and outward localization of ideas that 



tional activity . ,,.. ,.,..,. 



of the brain in- is, cerebral vision may take place by heightening or re-en- 

 creases them. f orc i n g the old impressions, as well as by diminishing the 

 intensity of the new sensations ; and as in the former case, so in this, the 

 result can be reached in many different ways. Whatever will cause in- 

 creased functional activity of the cerebral structure may recall these old 

 images in force. It is almost unnecessary to allude to the delirium 

 which attends inflammatory states of the brain. Artificial experiments 

 are more instructive. 



For the purpose of increasing the functional activity of the cerebral 

 Case of protox- structure, protoxide of nitrogen, by reason of its greater solu- 

 ide of nitrogen, bility in the blood, exceeds in power even oxygen gas itself. 

 This substance, when respired, at once awakens long trains of vivid ideas, 

 the recollection of all kinds of former scenes. Its action is divisible into 

 two periods, the first corresponding to the heightened sensibility arising 

 from the increased oxidation it is establishing in the economy, the sec- 

 ond to the depression which soon comes on through the consequent ac- 

 cumulation of carbonic acid, and which the lungs and skin are unable 

 with sufficient quickness to remove. Sir H. Davy, who first recognized 

 its physiological power, has given us a graphic description of these ef- 

 fects. He says, "A thrilling, extending from the chest to the extremir 



