CHAPTER II 



ORGANIC SUBSTANCES AND THEIR 

 CHEMICAL CHARACTERS 



ALL the activities of life depend upon protoplasm, 

 which is therefore the essential part of every living 

 organism. But by no means all parts of an organism 

 consist of or contain living protoplasm. For instance, 

 the heartwood and outer bark of a tree, the hairs, 

 feathers, nails or hoofs of a warm-blooded animal are 

 destitute of protoplasm. These lifeless parts of an 

 organism are, however, all formed from or by proto- 

 plasm, and they consist mainly of complex chemical 

 compounds, containing carbon, hydrogen and oxygen, 

 often also nitrogen and sulphur, as well as other elements, 

 which are called " organic " compounds because they 

 are associated with organisms. There is no sharp 

 distinction between organic and inorganic compounds 

 in chemistry, and many of the simpler organic compounds 

 formed by organisms can also be made synthetically 

 in the laboratory. 



All the organic compounds contain the element 

 carbon, organic chemistry being sometimes known as 

 " the chemistry of the carbon compounds," though 

 many substances containing carbon (for instance, cal- 

 cium carbonate) are not specially associated with 

 organisms. Of the immense number of organic com- 

 pounds known certain classes are specially important 



in the structure and activities of living organisms, and 



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