198 The English School [lect. 



His nitro-aereal hypothesis also enabled him to lay hold of a 

 sound theory of animal heat. 



The union of the nitro-aereal particles (taken in by breathing) 

 with the salino-sulphureous particles of the blood gives rise to 

 the heat of the blood. The greater heat which accompanies 

 violent exercise is due to the greater supply of nitro-aereal 

 particles caused by the increased respiration. This brings 

 about an increased effervescence, and so an increase of heat 

 in the blood itself, but at the same time the heat is also in- 

 creased by the greater effervescence in the muscles themselves. 



It will thus be seen that Mayow had laid firmly hold of one 

 factor of respiration, the entrance of something from the air of 

 the pulmonary vesicles into the blood. He had not grasped the 

 other factor now known to us, the exit of something from the 

 blood into the pulmonary vesicles. He was only on the track 

 of this. He says, "about expiration is to be noted that this 

 " serves a further purpose, namely, that together with the air 

 " driven out of the lungs, the vapour of the blood agitated by 

 " the fermentation is blown away also." And he developes a 

 theory, foreshadowing modern views, that it is a feature of the 

 fermentative action of the nitro-aereal particles that the blood, 

 when it comes back to the lungs as venous blood, having been 

 deprived in the tissues of its nitro-aereal particles, is greedy of 

 fresh particles of that kind, and so assists in drawing them into 

 the blood out of the air of the lungs. So the fermentation of 

 the blood is kept up by an automatic, self-regulating process. 



I have ventured to dwell at such length on the writings of 

 John Mayow because they afford a striking example of how 

 the seed of truth fails to spring up into a plant unless it 

 fall on congenial ground. By his nitro-aereal, or igneo-aereal 

 particles, Mayow evidently meant what we now call oxygen. 

 He saw that this formed only a part of the atmosphere, that 

 it was essential for burning, that it was essential for all the 

 chemical changes on which life depends, that it was absorbed 

 into the blood from the lungs, carried by the blood to the 

 tissues, and in the tissues was the pivot, the essential factor of 

 the chemical changes by which the vital activities of this or 

 that tissue are manifested. It was essential in muscle to the 



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