CHAPTER XVII 



THE MYSTERY OF THE CELL 



I HAVE already (at page 292) given a short account of the 

 chemical composition of protoplasm — the highly complex 

 substance now held to be the physical basis of life, and by 

 one school of biologists alleged to explain, as a result of 

 that complexity, all the wondrous phenomena of growth 

 and development. I now propose to give a very brief sketch 

 of the physical characteristics of the living cell, of its internal 

 structure, and of the extraordinary internal changes it under- 

 goes during the growth or reproduction of all organisms. 



One of the lowest or most rudimentary forms of life 

 is the Amoeba, a living cell, just visible to the unaided eye 

 as a little speck of floating jelly. This creature, being one 

 of the most common of living microscopic objects, will have 

 been seen by most of my readers. At first, under a low 

 microscopic power, it appears structureless, as it was for 

 some time described to be, but with increasing power and 

 perfection of the microscope it is found to consist of three 

 parts — a central body of a nearly globular shape slightly 

 darker and more granular in texture, the outer jelly-like 

 mass, and a small more transparent globular portion, which 

 looks like an air-bubble, and is seen to undergo a slow 

 motion of contraction and expansion ; this is termed the 

 " contractile vacuole," which, when it has reached its full size, 

 perhaps a quarter or a fifth of the whole diameter, suddenly 

 disappears, and after a little while reappears and gradually 

 grows again to its maximum size. The shape of the 

 Amoeba varies greatly. Sometimes it is globular and 

 immovable, but most frequently it is very irregular with 

 arm-like processes jutting out in various directions. By 



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