A HISTOEY OF METABOLISM 23 



obtained are nearly the same, we can conclude directly and without 

 hypothesis that the conservation of animal heat in the animal body is due, 

 at least in greater part, to the transformation of 'air pur' (oxygen) into 

 'air fixe' (carbonic acid) during the process of respiration." Here 

 be it noted that Lavoisier refers to the conservation of animal heat more 

 than fifty years before the general law of the conservation of energy was 

 enunciated. He also observed that two sparrows produced about the 

 same quantity of carbonic acid in the unit of time as did a guinea-pig. 



About a year after these experiments (1781) Cavendish in England 

 found that when "inflammable air" (or hydrogen) and Priestley's "de- 

 phlogisticated air" were united by an electric spark the airs disappeared 

 and water resulted. 



It is said that Lavoisier, hearing of these experiments from Blagden, 

 secretary of the Royal Society of London, repeated them. But the im- 

 portant point is that Lavoisier (d) was the first really to understand the 

 phenomenon. In a memoir presented to the Academic des Sciences in 

 1783 he stated that water is merely a combination of "inflammable air" 

 and oxygen and that any heat or light produced by their union is 

 imponderable. 



In the same year Lavoisier (e) completely demolished the phlogiston 

 hypothesis and concluded his memoir "Reflections upon Phlogiston" with 

 these words : 



My object in preparing this memoir has been to record the new developments 

 of the theory of combustion which I published in 1777, to show that the phlogiston 

 of Stahl, which he gratuitously supposed existed in metals, sulphur, phosphorus 

 and all combustible substances, is an imaginary creation. All the phenomena 

 of combustion and calcination are much more readily explained without phlogis- 

 ton than with phlogiston. I understand that my ideas will not be suddenly 

 adopted. The human mind conforms to a certain manner of vision and those 

 who during a portion of their lives comprehend nature from a given point of 

 view have difficulty in acquiring new ideas. In good time the opinions I have 

 set forth will be confirmed or destroyed. In the interim, it is a great satisfaction 

 for me to see that young, unprejudiced minds among those who are commencing 

 to study science, such as mathematicians and physicists who have a new sense 

 of chemical truths, no longer believe in phlogiston as presented by Stahl but 

 regard the whole doctrine as scaffolding which is more embarrassing than it is 

 useful for the continuance of the structure of the science of chemistry. 



And the wonder of it all is that the great chemists of his time outside 

 of his own country persisted in their narrow viewpoint. Priestley and 

 Cavendish refused to be converted. Scheele wrote in 1783, "Is it im- 

 possible to convince Lavoisier that his system will not find universal 

 acceptance? The idea of nitric acid from nitrous air and pure air, of 

 carbonic acid from carbon and pure air, of sulphuric acid from sulphur 

 and pure air, of lactic acid from sugar and pure air ! ! Can one believe 

 such things ? Rather will I support the English." 



