ix] Doctrines of Respiration. 241 



sense that he did not discover the true nature of the substance 

 which he had prepared ; what he did discover was that the air 

 which he had prepared was that part of common air which sup- 

 ported combustion and life. 



By the help of this discovery he could now explain on the 

 phlogiston theory his previous results. 



Animals whose bodies abound in phlogiston, introduced by 

 their food (for both the dead food and the body which eats the 

 food are combustible, and combustible means holding phlogiston), 

 in the act of breathing give out phlogiston so long as the 

 atmosphere they breathe contains enough dephlogisticated air 

 to absorb the phlogiston ; when this dephlogisticated air becomes 

 saturated with phlogiston and can receive no more, the atmo- 

 sphere ceases to be respirable. 



Animals can take in, can imbibe phlogiston only as part 

 of their food, can take it in only when it is already combined 

 with the substance of their food. Plants, on the other hand, 

 under the influence of light can imbibe phlogiston directly from 

 the air, can withdraw phlogiston from and so dephlogisticate the 

 air ; hence it is that they can render respirable or dephlogisticated 

 the air which animals have rendered irrespirable or phlogisti- 

 cated. But they can do this only under the influence of light. 



" In these experiments," his experiments on air, " it clearly 

 " appeared that respiration is a phlogistic process affecting air 

 " in the very same manner as every other phlogistic process (viz., 

 "putrefaction, the effervescence of iron-filings and brimstone, 

 " or the calcination of metals, &c.) affects it ; diminishing the 

 "quantity of it in a certain proportion, lessening its specific 

 " gravity, and rendering it unfit for respiration or inflammation, 

 " but leaving it in a state capable of being restored to a tolerable 

 " degree of purity by agitation in water, &c." 



The last words in the above sentence refer to some earlier 

 experiments made before he had observed the restoration of 

 vitiated air by vegetation, experiments which led him to think 

 that he could obtain a certain amount of restoration by mere 

 agitation with water. 



He many times insists that respiration and putrefaction are 

 the same things. 



o 

 F. L. 16 



