PRELIMINARY IDEAS. 5 



elements, namely, carbon, hydrogen, oxygen, and azote or 

 nitrogen. Such bodies decompose rapidly by becoming putrid 

 when exposed for a certain period to moisture and warmth. 

 They differ also from the others in respect of their molecular 

 constitution, inasmuch as each atom of an organic matter 

 results from the union of many atoms of organized matter, 

 whilst an atom of a mineral body results from the union of 

 but a few. An atom of carbonic acid, for example, is formed 

 of 1 atom of carbon united to 2 atoms of oxygen ; whilst 1 

 atom of stearine (a kind of fat) seems to contain 140 atoms 

 of carbon, 134 atoms of hydrogen, and 5 atoms of oxygen. 



Now these organized materials form the basis of all the 

 living parts of animals and plants, whilst the inorganic or 

 mineral play only a secondary part in the economy of these 

 beings. Chemically, then, these four elements characterize all 

 living bodies, nothing similar occurring in the mineral 

 kingdom. 



10. Thus living bodies differ from the inorganic by their 

 chemical composition, internal structure, general conforma- 

 tion, mode of origin, mode of existence, and manner of destruc- 

 tion. But to characterize them briefly, it is sufficient to say that 

 they are beings which are nourished and reproduced, these 

 being the most remarkable of vital phenomena. It is the pre- 

 sence of life, then, which especially characterizes plants and 

 animals, of which the simplest expression is to be nourished. 



11. Respecting the nature of life, science has no data ; 

 but as in physics the cause of heat is, as it were, personified 

 under the name of caloric, so in physiology a special force is 

 admitted as the cause of phenomena wholly inexplicable by 

 the ordinary laws of physics ; this is called the vital force. 

 Even its laws are beyond calculation, and we can only trace 

 some of the circumstances which seem essential to its mani- 

 festation. Thus, by desiccation, life is suspended in certain 

 animals and plants, and reappears when the requisite moisture 

 has been supplied. Another condition of life is, a certain 

 temperature and the influence of the air. 



12. Organs. Life manifests itself through the medium 

 or by means of organs or instruments, more or less numerous, 

 constituting the body of the animal or plant. Between the 

 organs and the functions they perform there is a necessary co- 

 relation ; the muscles, for example, are the immediate instru- 

 ments or organs of motion ; while the organs of sense inform 

 us of what surrounds us. 



