VI PREFACE. 



aware that Prof. Liebig has made any claims in this direction, yet 

 it can scarcely be doubted that his original researches in Animal 

 Chemistry tended strongly toward the promotion of the science of 

 Tital dynamics. 



The work of Professor Grove, which is here reprinted in full, 

 has a high European reputation, having passed to the fourth edi- 

 tion in England, and been translated into several continental lan- 

 guages. It is hardly to the credit of science in our country, that 

 this is the first American edition. The eloquent and interesting 

 paper of Helmholtz, though delivered as a popular lecture, was 

 translated for the Philosophical Magazine, and has been very highly 

 appreciated in scientific circles. Th% three articles of Mayer, 

 which were also translated for the Philosophical Magazine, will 

 have interest not only because of the great ability with which the 

 subjects are treated, but as emanating from a man who stands per- 

 haps preeminent among the explorers in this new tract of inquiry. 

 The researches of Faraday in this field have been conspicuous and 

 important, and his argument is marked by the depth and clearness 

 which characterize, in an eminent degree, the writings of this ex- 

 traordinary man. The essay of Liebig forms a chapter in the last 

 edition of his invaluable ' Familiar Letters on Chemistry,' which 

 has not been republished here ; and, as it touches the relation of the 

 subject to organic processes, it forms a fit introduction to the final 

 article of the series by Dr. Carpenter, on the " Correlation of the 

 Physical and Vital Forces." The eminent English physiologist has 

 worked out this branch of the subject independently, and the pa- 

 per quoted gives evidence of being prepared with his usual care 

 and ability. A certain amount of repetition is of course unavoida- 

 ble in such a collection, yet the reader will find much less of this 

 than he might be inclined to look for, as each writer, in elaborating 

 the subject, has stamped it with his own originality. 



In the introduction I have attempted to bring forward certain 

 facts in the history of these discoveries, in which we as Ameri- 

 cans have a special interest, and also to indicate several applications 

 of the new principles which are not treated in the volume. It 

 seemed best to confine the general discussion to those aspects of the 

 subject upon which most thought had been expended, and which 

 may be regarded as settled among advanced scientific men. But 

 there are other applications of the doctrine, of the highest interest, 

 which though incomplete are yet certain, and these will bo found 



