xiv AUTHOU'S PREFACE. 



the carbonic acid always increases relatively with the urea^ or in 

 certain cases Mitli the uric acid^ and if further, we possessed 

 experiments illustrative of the effects of diseases, and of varied 

 diet on the bile, we should then have a more solid basis than 

 we now occupy, -on which to found our chemical inquiries, 

 while the acquisition to the science of medicine would be po- 

 sitive and incalculable. The questions here involved must, 

 however, unfortunately, at the present time, be regarded as 

 unanswerable. We cannot doubt that the pulmonary exhalation 

 does vary, under different circumstances, in the amount of car- 

 bonic acid; for instance, more carbonic acid is exhaled during 

 prolonged corporeal exertion than when the body is in a state 

 of repose ; although, as far as I am aware, no experiments on 

 this subject have yet been instituted.' We have, however, con- 

 clusive evidence that the amount of urea is increased under 

 these circumstances. 



On the other hand, in the researches of Trommer regarding 

 the passage of sugar into the portal blood of horses, this sub- 

 stance could not be detected in the chyle nor in the arterial or 

 venous blood, which renders it more than probable that the 

 liver not only serves the purpose of modifying the composition 

 of the blood, but likewise effects the object of altering or re- 

 moving abnormal substances from it that have been absorbed 

 by the mesenteric veins. Hence this organ appears, in a cer- 

 tain degree, to take a share in the process of digestion, an 

 opinion supported by Berzelius. Future investigations re- 

 specting the functions of the liver may lead to very important 

 results, and throw much light on many of the most obscure 

 departments of physiology. 



Although very little has }^ct been done in physiological and 

 pathological chemistry, the rational physician, who ventures to 

 cast aside the trammels of dogmatism and empiricism, cannot, 



' [The experiments of Schariing on this subject were made after the publication 

 of the ' Chemistry of Man.' A brief notice of them is given in p. 129 of this volume.] 



