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1905] BARNES—THE THEORY OF RESPIRATION 83 
on account of the notable revolution in chemistry which took place 
about this time. INGENHOUss, the Dutch naturalist, really ascer- 
tained and published in 1779 the chief external facts of respiration; 
at least he was able,to state them essentially as they were known 
for twenty-five years “alter his time. In 1804, DESAUSSURE showed 
that growth is dependent on respiration; that respiration is more 
active in growing parts than elsewhere; that it is the cause of the 
loss of weight to which plants are constantly subject; and later, that 
the heat set free in flowers is related to the absorption of oxygen. 
Not until 1833 was respiration treated comprehensively, when 
DUTROCHET expounded the subject, comparing the respiration of 
animal and plant, and showing it to be fundamentally alike in both. 
Now at this point there began two remarkable misconceptions. 
One was the confusion that arose between respiration and the manu- 
facture of carbohydrates, which DuTRocHET called “diurnal respi- 
ration.” Of that I shall not speak, save to say that the great weight 
of Liesic’s authority made this error persist for half a century. 
RESPIRATION AND COMBUSTION. 
The other misconception was engendered by the comparison of 
respiration to combustion. It had been observed by LAVOISIER 
that the heat of the animal body was dependent upon respiration; 
the heat of the plant body was shown by DESaussvReE to be related 
to a disappearance of oxygen; combustion consumes oxygen and 
produces heat; therefore, respiration is a sort of combustion. So 
the argument ran. 
It is quite impossible to overestimate the influence that this con- 
ception has had on the study of respiration. The mischief it has 
wrought depends chiefly, perhaps wholly, upon a misconception of 
the actual mechanism of combustion, a process that has ever been 
the béte noire of chemistry, as the history of the “phlogiston” theory 
well shows. To our changed conceptions of combustion I shall 
return later. 
The idea of combustion, however, which dominated the argument 
I have cited, was that oxygen combined with carbon to form CO, 
and with hydrogen to form H,O. It was most natural, therefore, 
to conceive that the food taken up by the organism stood to it in 
