PREFACE. 



THE subject of the respiratory exchange of animals is not one 

 of physiological chemistry but rather of chemical physiology. 

 It deals with very few substances, and with their quantities not 

 their qualities. The relations between respiratory exchange 

 and functional activity have been excluded from the scope of 

 the present monograph, which deals therefore with one very 

 limited problem only : the quantitative aspect of the catabolic 

 activity of the living organism as living. 



To give an exhaustive account of the work done even in 

 this restricted field has not been attempted, but I have endeav- 

 oured to trace out the essential lines of study, to state the 

 fundamental problems, and to indicate the solutions of them so 

 far as such solutions appear to have been reached with what 

 amount of success it is for the reader to judge. 



For my own part I have felt the difficulties of my task so 

 acutely that I cannot doubt but that they must have been very 

 imperfectly overcome, and I shall be very grateful to have 

 errors and omissions pointed out to me. 



AUGUST KROGH. 



COPENHAGEN, September, 1915. 



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