42 ORGANIC SUBSTANCES : CHEMICAL CHARACTERS 



cottonseed, coconut, castor oil seed. They contain an 

 even larger store of potential energy per molecule than 

 the carbohydrates, and thus require more oxygen for 

 complete oxidation. Of numerous kinds two examples 

 are palmitin (CgiHggOg) and olein (CsyH^oi'^e)- ^^*s 

 occur in plant cells as complex mixtures of different 

 individual fats. They are usually found in the liquid 

 state, and are then often spoken of as " oils." 



Fats are even more widespread and important in the 

 animal than in the plant body, forming a very valuable 

 reserve store of energy. 



The Proteins. 



These are the most important of the nitrogen- 

 containing organic substances. The molecule consists 

 of carbon, hydrogen, oxygen, nitrogen and sulphur, 

 with sometimes phosphorus in addition. The protein 

 molecules are the largest and most complex of any 

 chemical compounds, each molecule consisting of many 

 hundreds, or even thousands, of atoms. The different 

 groups of atoms composing these huge molecules have, 

 like the atoms composing the molecules of all chemical 

 compounds, a perfectly definite position in regard to 

 one another. The more numerous the atoms the greater 

 will be the number of different relative positions possi- 

 ble. Hence there are an enormous number of distinct 

 protein molecules with comparatively small differences 

 between them. 



Now protein molecules form the essential basis 

 of protoplasm. Protoplasm, as we shall see in 

 succeeding chapters, has the same general character- 

 istics and powers in all living organisms, but it is 

 obvious that the protoplasm of every species differs 

 in some way from that of every other species, or it 



