CHAPTER 3 

 SOME FUNDAMENTAL PHYSICS AND CHEMISTRY 



In the activities of cells, great importance is to be attached to that 

 very fine, mostly invisible, structure which inheres in the chemical 

 composition and minute physical constitution of the protoplasm itself. 

 These features of protoplasm are appropriately discussed along with 

 the physiological processes which depend on them. Such processes 

 should next engage our attention. Since, however, an understanding of 

 this minute structure presupposes a knowledge of elementary chemistry 

 and physics, it is advisable to pause a moment to acquire some of the 

 more important ideas in that field. 



Composition of Matter. — The physical substance of which objects 

 are composed is called matter. Matter exists in a number of different 

 forms called elements. An element is a svibstance possessing a character- 

 istic structure which is different from that of every other element and 

 which cannot be broken down into substances different from itself (that 

 is, into other elements) by ordinary chemical means. The stipulation 

 "ordinary chemical means" is intended to exclude radioactivity and 

 powerful electronic machines. Among the more common elements 

 entering into the composition of living things are carbon, nitrogen, 

 oxygen, and hydrogen. 



The elements may exist by themselves, chemically separate from 

 other elements, as do oxygen and nitrogen in the air. More often they 

 exist in compounds; these are distinct substances, made up of two or 

 more elements, joined in definite proportions and with characteristic 

 internal structure. Carbon dioxide is a very stable compound, made 

 of carbon and oxygen, which is eliminated as a waste product by all 

 living things. Calcium carbonate, of which bones are largely built, is a 

 compound composed of three elements: calcium, carbtm, and oxygen. 



Both elements and compoimds are divisible into molecules. These 

 are the smallest imits of a substance in which its characteristic chemical 

 structure is maintained. The molecules are likewise the smallest units 

 which exhibit the chemical properties of that substance. If a molecule 

 is divided or broken up, its parts no longer have those properties. The 

 elements which enter into a compound are present in each molecule in 

 the same proportion as in large masses of the substance. Each molecule 

 is exactly like every other molecule of the same substance, not only in 



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