312 Dr. Edwards, Dc V Influence 



averted by clothing. Among the parts exposed to light, the 

 eyes are specifically adapted to its reception, but not so 

 exclusively relative to reflection of objects of vision. Light 

 must be considered as entering by means of the eyes into the 

 system, as by corporeal contact elsewhere. The exquisitely 

 sensible condition of these organs renders them the most 

 vivid portions of the nervous sj^stem, for the transmission of 

 light and its influence upon the animal economy in general. 

 In many acute disorders, light striking upon the eyes not 

 only excites vision, but produces an exacerbation in the 

 whole system. 



Having disposed of this agent, Dr. Edwards proceeds to 

 examine into the alterations which the air undergoes by re- 

 spiration, such as the displacement of oxygen, and the sub- 

 stitution of carbonic acid, with the inspiration and expiration 

 of azote. Experiments are brought forward to illustrate 

 the proportionate exhalation and absorption of azote, and 

 the evolution of carbon during respiration. The results may 

 be shortly summed up in the following manner. The oxygen 

 displaced in respiring atmospheric air is entirely absorbed ; 

 subsequently it is carried altogether, or in part, into the 

 stream of the circulation ; its dislodgment from the air 

 respired is replaced by a quantity more or less equal to it of 

 carbonic acid exhaled from the lungs, derived entirely or in 

 part from what is contained by the mass of the blood. Also, 

 an animal breathing atmospheric air absorbs nitrogen (azote), 

 which is carried into the mass of the blood entirely or par- 

 tially, where it constitutes the basis of several animal sub- 

 stances ; the residue apparently going off by the kidneys, 

 when more is introduced into the system than is wanted. 



The importance and complication of the respiratory func- 

 tion are here pointed out, and we learn also that it is one 

 not merely of a chemical character, a simple act of pulmo- 

 nary combustion ; but attended with several vital actions, as 

 absorption, exhalation, &c. 



The blood of the animal body, therefore, contains gases de- 

 rived from respiration of atmospheric air, but not solely from 

 this source. During digestion there is more or less gas evolved 

 in the intestinal canal, which is a subsidiary source, and 

 absorbed from the surface of the mucous membrane. As one 

 proof of this fact, we may refer to the effect of copious 

 draughts of water impregnated with carbonic acid gas, 

 having been known to produce asphyxy. 



Dr. Edwards concludes his researches with a chapter de- 



