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reach of anatomical than chemical investigation. The present theory 

 among chemists, he states, is, that respiration decarbonizes the blood, 

 a volume of oxygen and nitrogen being at each inspiration received 

 into the lungs, and returned, measure for measure, the oxygen only 

 being partly converted into carbonic acid ; thus proving, as they sup- 

 pose, that no part of the atmospheric air breathed is retained. 



This theory he considers as satisfactory, supposing it supported by 

 the structure of the lungs themselves, and taking it for granted that 

 the blood requires no other change for its purification. But when it 

 was devised, no accurate examination of the cellular structure of the 

 lungs had been set on foot ; and it is the object of this paper to ex- 

 plain their mechanism, and see how far it is fitted for the processes 

 this theory requires. 



The author began by inquiring into the circulation of blood through 

 the lungs ; and by the aid of Mr. Russel procured injections of their 

 veins and arteries, capable of being rendered objects of microscopic 

 investigation by Mr. Bauer. 



The first fact discovered was, that though an injection introduced 

 by the pulmonary artery was found to return by the trunks of the 

 pulmonary veins, yet, when thrown in by the veins, it does not re- 

 turn by the arteries. 



The next fact ascertained was, that the distention of the air-cells 

 produces an interruption between the arterial and venal circulation, 

 the blood being carried no further than the small arterial branches 

 surrounding the air-cells. 



The author then proceeds to describe the air-cells and parts sur- 

 rounding them, from drawings made by Mr. Bauer. The branches 

 of the pulmonary artery, accompanied by larger and more numerous 

 branches of the pulmonary vein, are seen ramifying behind the in- 

 ternal membrane of each cell. The latter have valves at regular in- 

 tervals, and there are also numerous absorbents supplied also with 

 valves. The injection was found to have stopped short of the termi- 

 nation of the artery, and the space beyond to be filled with gas. 



After this description, and after expressing his obligations to Mr. 

 Dollond for his improvement in the microscopes used by Mr. Bauer, 

 the author proceeds to deduce his conclusions, which are unfavour- 

 able to the received doctrine of simple decarbonization, conceiving the 

 structure thus developed as better adapted to receive supplies from 

 the atmosphere, and transmit them to the heart. He considers that 

 the carbonic acid, detected by Professor Brande, in urine and per- 

 spirable matter, must have been formed in the blood circulating 

 through the arteries, and have derived its oxygen from the lungs. He 

 considers, further, that the carbonic acid carried off in respiration, is 

 furnished from such venous blood as has acquired it during the pro- 

 cess of digestion ; having known on a former occasion that soon after 

 that process has been begun, the oxygen employed in it unites with 

 carbon. 



He finally remarks that, for carrying on the functions of life, and 

 for supplying oxygen and removing carbon, respiration is necessary, 



