

CHAPTER II. 



THE COMPOSITION OF LIVING ORGANISMS. 



Living and Lifeless Matter in the Living Organism. Since our 

 own bodies and those of lower animals and of plants are com- 

 posed of matter, it might be supposed, from what has been said 

 in the last chapter, that they are composed of living matter. 

 This, however, is true only in part. It is strictly true that every 

 plant or animal contains living matter, but a little reflection will 

 show that it contains lifeless matter also. In the human body 

 lifeless matter is found in the hairs, the ends of the nails, and 

 the outer layers of the skin, structures which are not simply de- 

 void of feeling, as every one knows them to be, but are really 

 lifeless in every sense, although forming part of a living body. 

 Nor is lifeless matter confined to the exterior of the body. The 

 mineral matter of the bones is not alive ; and this is true, though 

 less obviously, of many other parts, such as the liquid basis of 

 the blood, or plasma, the fat (which is never wholly absent) and 

 various other forms of matter occurring in many parts of the 

 body. 



In lower animals examples of this truth occur on every hand. 

 The calcareous shells of animals like the snail and the oyster; 

 the skeletons of corals and sponges ; the hard outer crust of in- 

 sects, lobsters, and related animals ; the scales of fish and reptiles ; 

 the feathers, claws, and beaks of birds; the fur of animals; 

 these are a few of the countless instances of structures composed 

 wholly or in part of lifeless matter, which nevertheless enter into 

 the composition of living animals. 



Among plants like facts are even more conspicuous. No one 

 can doubt that the outer bark of an oak is devoid of life. The 

 heart-wood of a tree is entirely dead, and even in the so-called 

 live wood, through which the sap flows, not only is the solid part 

 of the wood lifeless, but also the sap itself. 



In short, it is a general truth that the living matter of plants 

 and animals is almost invariably associated with lifeless matter ; 



