20 INTRODUCTION. 



animals ; it belongs to psychology to study and make known 

 the faculties which separate him from them." 1 



Even without accidents, physiological death is a necessity 

 of existence ; but nature has provided, as one of the most im- 

 portant attributes of organization, a means by which organ- 

 ized bodies may be perpetuated through all ages. In the fully- 

 developed organism are produced two kinds of organic ele- 

 ments, the male and the female. These, when brought in 

 contact with each other under proper conditions, are capable 

 of being developed into a new being, similar in organization 

 to, and designed to take the place of, the one which is to pass 

 away. These new beings are generated in sufficient number 

 to insure the perpetuation of the species. 



The excrementitious products of the body during life, and 

 the body itself after death, changed by the peculiar process 

 of putrefaction, are returned to the earth and to the air, and 

 contribute to the nutrition of the vegetable kingdom. The 

 vegetables, in their turn, are consumed in the nutrition of 

 animals. All the elements necessary to nutrition, except 

 oxygen, are taken into the alimentary canal as food. Our 

 food consists either of vegetables, or the flesh of animals that 

 are nourished by vegetables. 



PROXIMATE PRINCIPLES. 



From the preceding general remarks, it is evident that 

 physiology, to be systematically and properly studied, must 

 be connected with physiological anatomy and chemistry. 

 The physiological anatomy of special organs and systems 

 naturally precedes the consideration of their functions ; and in 

 treating of the functions of other parts, more especially the 

 nutritive and excrementitious fluids and the secretions, we 

 are unavoidably led to consider fully their chemical constitu- 

 tion. There are, however, certain constituents of the body, 



1 LONGET, Traite dc Physiologic, Paris, 1861, tome i., p. xxviii. 



