de$ Agens Physiques sur la Vie, 141 



that, while It was among the first to be noticed, it has been 

 the latest in producing satisfactory results. Among the 

 opposing causes of the advancement of knowledge in this 

 department, the ignorance of our ancestors in chemical 

 science seems to be the principal. Without chemical aid it 

 is perfectly useless to attempt the investigation. The com- 

 position of the air respired must be well understood ; the 

 different gases must be carefully examined, or the physiolo- 

 gical inquiry will be darkened and obscured. 



Dr. Priestley laid the foundation of our chemical know- 

 ledge of gases in their relation to respiration ; but some time 

 elapsed before it was understood in what manner the air 

 was connected with animal organisation. Oxygen gas, one 

 of the known constituents of atmospheric air, was Priestley's 

 discovery, in its effect upon the blood, of converting this 

 fluid from a dark purple to a bright crimson. Lavoisier 

 founded a chemical theory upon this discovery of the agency 

 of air, which was subsequently applied by Goodwin to phy- 

 siology. The latter author demonstrated, by a series of 

 excellent and correct experiments, that the exclusion of 

 atmospheric air produces death in animals, in consequence of 

 the dark-coloured blood usually circulating in the veins being 

 prevented from becoming crimsoned. The state in which 

 any animal may be thus placed, is known by the term 

 ASPHYXY, and by which is to be understood a deficient or 

 suspended aerification of the blood, from whatever cause it 

 may proceed that the atmospheric air is prevented from 

 access to the blood as it circulates through the lungs. 



The great French anatomist, Bichat, pursued this subject 

 still farther, and published a treatise on Asphyxy. He 

 sought, by numerous experiments, to determine the threefold 

 relation of the air to the nervous system, respiration, and the 

 circulation ; and he arrived at this great and important 

 conclusion, that the venous or dark blood circulating 



THROUGH THE BRAIN, CREATES A CESSATION OF THE FUNC- 

 TIONS OF THAT ORGAN, AND THAT IN CONSEaUENCE THE 



HEART LOSES ITS ACTION. This discovery shows us at 

 once the direct cause of asphyxy in all its different degrees, 

 according, in effect, to the vitiated state of the blood from 

 its deficient or suspended aerification. 



Le Gallois also investigated the subject of asphyxy ; and 

 he found that, when dark blood circulated through the spinal 

 marrow , the motions of the heart ceased ; and thus he not 

 only determined the relations of the nervous system to atmos- 

 pheric air, but also those of the respiration and the circula- 



