LECTUEE IX. 



THE RISE OF THE MODERN DOCTRINES OF 

 RESPIRATION. BLACK, PRIESTLEY, LAVOISIER. 



We have seen in a preceding lecture how far John Mayow 

 went in the knowledge of the chemistry of breathing. He 

 wrote in the third quarter of the seventeenth century ; and by 

 the end of the century his views had well-nigh passed away 

 from men's minds. Some writers it is true still spoke of 

 ' nitrous particles ' playing a part in breathing, but the ideas 

 which were thus put forth were more akin to the loose notions 

 which we have seen Sylvius held, than to the clear and definite 

 conception of Mayow. We have dwelt, in a preceding lecture, 

 on the chemical activity of Stahl, and, looking at the matter in 

 the light of our present knowledge, it seems difficult to under- 

 stand how it was that the foremost chemist of the early years of 

 the eighteenth century, who busied himself especially with the 

 nature of combustion and with the theor}' of phlogiston, did not 

 put forward some striking chemical theory of breathing. That 

 he did not do so seems to have been due to the way in which 

 his mind was influenced by views which he had adopted con- 

 cerning the physical and mechanical effects of the flow of blood 

 through the capillaries. 



Stahl taught that the most important fact about the 

 circulation of the blood was the passage through the capillaries, 

 the " transpression of the blood through the spongy, porous and 

 " exceedingly soft tissues of the body, by which doubtless it is 

 " kept constantly in a proper state of fluidity so that it may 



