88 Human Physiology. 







as to produce the particular odour, or make a distinct and 

 peculiar impression upon the nerve of smell. A grain of musk 

 will fill a room with musky particles by myriads for years, with- 

 out any perceptible loss of weight. The minute subdivision of 

 the virus of contagious diseases, such as small-pox, must be 

 evident. But organic nature aifords, after all, the most astound- 

 ing evidences of divisibility of matter. Thus 5^0,000 vibrios, 

 long, slender, worm- like, organised beings, are found in a single 

 grain of wheat; each one, of course, composed of multitudes 

 of atoms. One ounce of flesh has been found to contain 

 325,000 of those terrible parasites which are found in pork, 

 the trichinae, so that a man might contain 1,950,000.000. 



But even this is nothing to the minuteness of organic life in 

 infusoria, of which a cubic inch of water may contain 8,000,00.0. 

 What then must be the size of the atoms of which they are 

 made; of the water in which they live, feed, and multiply; of 

 the elements, oxygen and hydrogen, which compose it? 



Such is the infinite or immeasurable minuteness of all the 

 matter that makes up the material world. No one can tell how 

 small an atom is, but eminent physicists have calculated that 

 an atom must be less than i-6,ooo,oooth of a line in diameter, 

 and that it must take at least 888,490,000,000,000 atoms of 

 lead to make a cubic inch. 



Chemistry has discovered more than sixty elementary bodies, 

 or distinct kinds of matter, which have not been resolved into 

 more simple elements. But it is the belief of many eminent 

 physicists that all these may be composed of only one element, 

 or one kind of atoms, which group in different ways to form 

 the molecules of all kinds of matter. Suppose, for example, 

 that hydrogen, the gas that fills balloons, the lightest of known 

 substances, is this primitive matter, then oxygen would be 

 composed of molecules, each made of eight atoms of hydrogen, 

 and so on. 



The simple elements of matter combine together to form all 



