10 PRINCIPLES OF PHYSIOLOGY. 



of animal nature ; but since every animal is not provided with 

 those animal forces, which the most perfect possess, in the 

 Second Chapter the different genera of animals are classified 

 from the irrational to the rational. I have taken this oppor- 

 tunity to state reasons for the possibility and existence of 

 animals without souls. The other Chapter of this Part treats 

 of the origin, life, maturity, decline, and death of animal nature. 

 Hitherto we have only had scattered notices of these various 

 matters in our physiological works, or, at most, of the peculiar 

 mechanism of generation ; and the growth, decline, and death 

 of animal organisms have only been considered, without sepa- 

 rating that which has reference to the proper animal nature 

 from the other portions of the subject. In this Part, the most 

 interesting chapters are the last three on the periods of animal 

 life, the system of animal forces, and on animal death; these 

 have a wide and useful application to the pathology of proper 

 animal nature. I have adopted a short, simple, dry, and me- 

 thodical plan of writing, that the reader may continually be 

 enabled to examine and thoroughly understand the truth of 

 the views and principles, both in the abstract and in their 

 application, — the connection and consequences of the doctrines, 

 — and the whole system of animal physiology. I have avoided, 

 as much as possible, all medical researches of a confusing, imper- 

 fect, or merely subtle character, and all hypotheses ; or, at least, 

 have made no use of the latter in establishing my own prin- 

 ciples ; for a system of presupposed ideas, which in a short 

 time must itself be set aside, would not be well received as a 

 commencement in this new division of medical science, instead 

 of true natural laws, the result of accurate observations. 



As to the doctrines themselves, and the various controversies 

 that have already arisen concerning them, I can only most 

 sincerely beg the reader to examine them with the greatest 

 rigour; and if the author of a work so extensive, and attempted 

 for the first time from the present point of view, have described 

 anything untruly, indistinctly, or incorrectly, or have omitted 

 anything, not to blame him too harshly. The justice of such 

 an exculpation can only be understood by those who have 

 undertaken to write on such a subject, and experienced the 

 difficulty of avoiding errors and omissions. I desire no in- 

 dulgence for the doctrines themselves. Truth has been sought. 



