PREFACE. 5 



"\Vith regard to the general mechanism of secretion, it 

 has seemed important to the author to draw as closely as 

 possible, the line of distinction between secretions proper 

 and excretions; and our information with regard to the 

 mode of formation of the secretions, and the production of 

 excrementitious principles and their separation from the 

 blood, is now of so positive a character, that we are able to 

 subject these processes to pretty definite generalization. 



If we comprehend fully the mechanism of secretion and 

 excretion, it is evident that our knowledge of particular 

 fluids must be to a great extent based upon accurate proxi- 

 mate analyses. The author has taken the greatest care in 

 compiling the tables of composition of the various secretions 

 and excretions, particularly with regard to the urine, having 

 endeavored to make the table of its composition repre- 

 sent as closely as possible the general process of disassimila- 

 tion and its variations under physiological conditions. 



The author cannot but regard the description of the 

 excretory function of the liver, with the discovery of the 

 physiological relations of cholesterine, as of very great im- 

 portance, in its relations to pathology as well as physiology. 

 This subject has been elaborately considered in the chapter 

 treating of the excretory function of the liver, and the views 

 therein presented are put forward with more confidence, 

 since they have been honored with a favorable report by a 

 committee from the French Academy of Sciences? As the 

 result of the author's investigations on this subject, it seems 

 to be conclusively proven that cholesterine, under certain 



1 ST. LAUGIER, Academic des sciences. Hole de la cholesterine dans Torganixme ; 

 recherche* de M. AUSTIN' FLINT (fils). Revue des cours scientifgues, Paris, 1868- 

 1869, tome vi., p. 495, and Comptes rendus, Paris, 1869, tome Ixviii., p. 1371. 



