XX 

 CHEMISTRY AND PROTOPLASM 



WHEN the chemist examines living cell-substance 

 or protoplasm as free as possible from dead 

 envelopes and products of its own activity so as to 

 make out, if he can, what it is chemically, he finds that 

 it consists of the elements carbon, oxygen, hydrogen, and 

 nitrogen, with some sulphur. Phosphorus and some 

 potash, soda and lime in small quantity, are also very 

 usually associated with the elements named. These are 

 combined in the protoplasm so as to form chemical 

 compounds resembling and including white of egg, and 

 are called " proteids." A chemical compound is a very 

 definite and special thing, and when one says so-and-so 

 is a definite chemical compound, one means that it is not 

 a mere " mixture," but is composed of chemical elements 

 (some out of the long list of about eighty indestructible, 

 undecomposable, " simple " bodies gases, liquids, metallic 

 and non-metallic solids recognised by chemists and 

 known as such), peculiarly united to, or " combined " with, 

 one another in definite proportions by weight. 



Take, as an example, water. Water is a definite 

 chemical compound, formed by the chemical union of 

 two pure elements, the gases hydrogen and oxygen 

 eighteen ounces of water consist of two ounces of 



hydrogen and sixteen ounces of oxygen. At a tem- 

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