COMPARATIVE ZOOLOGY. 



CHAPTER I. 



MINERALS AND ORGANIZED BODIES DISTINGUISHED. 



Nature may be separated into two great kingdoms — 

 that of mere dead matter, and that of matter under the 

 influence of life. 4 These differ in the following points : 



( 1 ) Composition. — While most of the chemical elements 

 are found in different living beings, by far the greater 

 part of their substance is composed of three or four — car- 

 bon, oxygen, and hydrogen ; or these three with the addi- 

 tion of nitrogen. Next to these elements, sulphur and 

 phosphorus are most widely distributed, though always 

 found in very small quantities. The organic compounds 

 belong to the carbon series, and contain three, four, or 

 five elements. The former class, comprising starch, sugar, 

 fat, etc., are relatively stable. The latter, possessing the 

 three elements named, with nitrogen and sulphur or phos- 

 phorus, are very complex, containing a very large number 

 of atoms to the molecule, and are usually unstable. Here 

 belong albumen, myosin, chondrin, etc., the constituents 

 of the living tissues. The formula for albumen is said to 

 be C 72 H 112 N 18 S0 22 , or some multiple of this formula. 

 These compounds also contain more or less water, and 

 usually exist in a jelly-like condition, neither solid nor 

 fluid. With these colloid substances alone is life associ- 

 ated. Only these can undergo the rapid decomposition 



