O PEEFACE. 



Our positive knowledge concerning many of the functions 

 considered in the present volume dates from important dis- 

 coveries. The author has in all cases made it his duty to 

 trace these discoveries to their original sources ; but in his 

 historical researphes, he has often found that the reputed 

 authors of important original observations had, generally 

 without their knowledge, been anticipated. The only object 

 in making references to the works of the earlier physiologists 

 has been to do justice, as far as possible, to every original 

 observer ; and all the works cited in foot-notes have, without 

 exception, been consulted by the author personally, in the 

 original, and the references clearly indicated. 



Most of the important. facts connected with the functions 

 of digestion and absorption have been repeatedly verified by 

 the author in his laboratory and in public demonstrations ; 

 and in many instances, the observations of others have been 

 more or less extended. The most important original obser- 

 vations, however, are upon the excretion of cholesterine in 

 the bile, and its transformation into stercorine in its passage 

 through the intestinal canal. In the present volume, this 

 question is considered in connection with the digestive func- 

 tion of the bile and the composition of the faeces. It will be 

 considered much more elaborately, under the head of Excre- 

 tion, in another volume. 



The succeeding volumes of the series will be devoted to 

 Secretion and Excretion, Nutrition, Movements, etc., the 

 Nervous System, and Generation. They will appear as 

 rapidly as is consistent with their careful preparation. 



NEW YORK, June, 1867. 



