RESPIRATION. 607 



up the motion of the heart and arteries. These views he illus- 

 trated and confirmed by many ingenious experiments, in which 

 he anticipated some of the modern discoveries respecting respi- 

 ration. 



Lower's work, De Corde item de Motu et Colore Sanguinis et 

 Chyli in earn Transitu, was published in 1669 ; or a year after 

 Mayow's tracts.* In this very ingenious treatise, he proves that 

 the florid colour of arterial blood is owing to the absorption of 

 air, or rather the nitrous spirit of air (oxygen) in the lungs. 

 This nitrous spirit is dissipated during the circulation. Hence 

 the reason of the dark colour which the blood has when it enters 

 the right auricle and ventricle before it passes to the lungs, where 

 it is again impregnated with air, and reassumes its florid colour. 



It is well known that carbonic acid gas was obtained in a se- 

 parate state by Dr Black, and that he ascertained that, when 

 passed through lime-water, it has the property of rendering it 

 turbid and milky. In the year 1757, by breathing through lime- 

 water, he ascertained that the air when thrown out of the lungs 

 contains carbonic acid.f In 1774, Dr Priestley discovered oxy- 

 gen gas, and found that animals could breathe it much longer 

 with impunity than the same bulk of common air. He found that 

 the quality of air was deteriorated by breathing precisely as by 

 combustion. According to him, when atmospheric air is com- 

 pletely deprived of phlogiston, it becomes oxygen gas ; when 

 completely saturated with phlogiston, it becomes azotic gas. 

 Blood exposed to air acquires a florid red colour, while, at the 

 same time, the air is deteriorated. Hence he conceived that the 

 use of respiration was to deprive the blood of phlogiston. : It is 

 curious, that, in the year 1776, he does not seem to have been 

 aware of the formation of carbonic acid gas during respiration, 

 though the fact had been noticed by Dr Black as early as the 

 year 1757. 



About the year 1780, Lavoisier published his experiments on 



* Yet Mayow quotes Lower in confirmation of his views. My copy of Mayow 

 is the second edition, printed (I believe, for the title-page is wanting,) in 1674 ; 

 and my copy of Lower is that in the Bibliotheca Anatomica, printed in 1685. 

 Doubtless additions were made to the new editions. Hence, unless we had the 

 original editions, it would be impossible to ascertain who first struck out the 

 ideas nearly identical stated by Thruston, Mayow, and Lower. 



f- Black's Lectures, ii. 87. f Priestley on Air, (first series), iii. 55. 



