i230 Medicine. 



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 pro- 

 cess of respiration. In order to explain this func- 

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

 basis, that all the changes produced on the air in- 

 spired are produced in the lungs; and, of conse- 

 quence, that all the new compounds and substances 

 detected in the air expired, are formed in the 

 lungs. It was a principle of this theory, that the 

 blood absorbs no air in the lungs; but that it dis- 

 charges hydrogen and carbon, which, combining 

 with the oxygen of the air inspired, form water 

 and carbonic acid. This theory was adopted by 

 La Place, Crawford, Gren, and Girtanner, 

 with some small modifications, which it is unneces- 

 sary here to particularize. Upon close inspection, 

 it appears that this theory of Lavoisier does not 

 materially differ from the original hypothesis of Dr. 

 Priestley, viz. that the object of respiration is to 

 free the blood of phlogiston. The difference con- 

 sists chiefly in terms and in detail. For if carbon 

 and hydrogen be substituted for phlogiston, which 

 is often necessary in reconciling the statement of 

 facts delivered by the phloglstlans and anflphlogls- 

 tlans, the two theories will be found entirely to 

 asree. M. Lwoisjer did little to establish his 

 theory by proof. He only attempted to prove that 

 the amount of oxygen absorbed in respiration ex- 

 actly corresponds with the quantity of it contained 

 in the carbonic acid and the water emitted. But 

 as this coincidence of quantities cannot be proved, 

 his theory is unsupported, so far as the establish- 

 ment of it depends upon such coincidence. 



Afterwards, when a greater number of facts and 

 illustrations of this subject had been collected, a 

 different theory was offered by La Grange. Ac-- 



