1290 Medicine. [Chap, IV. 



lungs. The principal of these are as follow : the 

 blood absorbs air ; it acquires a florid red colour, 

 and the chyle mixed with it undergoes such altera- 

 tion as to lose its colour and disappear; it emits 

 carbonic acid, and perhaps carbon itself; ar^d it 

 emits water, and perhaps hydrogen. The writers 

 who have principally signalised themselves in tra- 

 cing and making known these changes in the blood, 

 are Priestley, Cigna^ Fourcroy, Hassenfratz, Bed- 

 does, Watt, and, very lately, Mr. Davy. 



The tiieories of this function, as deduced from 

 facts successively discovered^ have varied according 

 to the number of such facts, and the impressions 

 which they made on different minds. Dr. Priest- 

 ley, the first of the modern chemical philosophers, 

 as was before remarked, who attempted to investt- 

 gate the use of respiration, seems to have consider- 

 ed it, from some of his earliest experiments, chiefly 

 as an excretory process. He believed that the 

 blood, in passing through the lungs, gives out 

 phlogislon to the air, which, when expired, he' sup- 

 posed to be loaded with that substance, and, con- 

 sequently, that the main purpose of respiration is 

 to discharge phlogiston from the blood. 



Soon after these conclusions had been formed 

 by Dr. Priestley, M. Lavoisier directed his efforts 

 to ascertain, with as much precision as possible, 

 the changes which the air undergoes in the process 

 of respiration. In order to explain this function 

 he framed a theory, which assumed, as its basis, 

 that all the changes produced on the air inspired 

 are produced in the lungs; and, of consequence, 

 that all the new compounds and substances detect- 

 <='d in the air expired, are formed in the lungs. It 



