ANIMAL JUICES. 9 



A larger portion of the systematic treatment of the animal 

 juices will be devoted to a consideration of the metamorphoses 

 experienced by each separate object within the living animal 

 organism, and the changes and decompositions observed in the 

 same substance external to the sphere of vitality. If we subjoin, 

 as in our notice of the animal substrata, those circumstantial data 

 which can alone justify us in considering the genetic development 

 of each object, we shall be in possession of all the elements, as far 

 as the present state of science permits, for forming an opinion 

 regarding the function or physiological value of every individual 

 animal fluid. By such a course, we shall certainly be carried 

 within the province of physiological processes ; but in considering 

 the metamorphosis of animal matter generally, and the processes 

 of digestion, respiration, and nutrition, in their systematic con- 

 nexion, our views of the chemistry of the animal body should not 

 be diverted to individual points, but rather be made to combine 

 with the conclusions obtained by simple induction, in reference to 

 the function of the individual chemical agents. (See Vol. T. p. 3.) 



If ever we cherished the hope of combining the results of 

 former inquiries into one scientific whole, constituting a purely 

 inductive branch of science, in accordance with our view of the 

 method in which physiological chemistry, and more especially the 

 theory of the animal juices, should be treated, our courage would 

 fail, as indeed it often has done, when we attempted the accom- 

 plishment of such a task. We believe that, in the first volume, we 

 have already sufficiently explained our view of the very great defi- 

 ciency of our knowledge in this department of the physical sciences ; 

 but here it is less a want of positive knowledge than a redun- 

 dancy of materials that renders it a matter of almost insurmountable 

 difficulty to demonstrate with clearness the pure and unadulterated 

 character of science free from pretentious delusions. A cursory 

 glance at the confused mass of materials accumulated before us, 

 presents a view of disorder requiring Herculean efforts to disen- 

 tangle them. We confess that we have therefore abstained from 

 attempting in the following pages to give the whole mass of the 

 results that have been obtained within this department of science 

 from all experiments and observations, whether good or bad; 

 limiting ourselves to facts collected by the best observers, which, 

 as far as our powers and experience permitted, we have compared 

 with the results of our own observations, testing the different 

 conclusions and hypotheses by a course of logical inquiry. With- 

 out reference to the present work, which we have designated as a 



