DEAD- AND LIVING BODIES. 3 



d. Mode of Increase. — ^When unorganised bodies increase in 

 size, as crystals do, the increase is produced simply by what is 

 called " accretion ; " that is to say, by the addition of fresh 

 particles from the outside. 



Organised bodies increase by what is often called the " in- 

 tussusception" of matter; in other words, by the reception of 

 matter into their interior and its assimilation there. To this 

 process alone can the term " growth " be properly applied. 



e. Cyclical Change. — Unorganised bodies exhibit no actions 

 that are not purely physical or chemical, and they show no 

 tendency to periodical vicissitudes. Organised bodies are pre- 

 eminently distinguished by the tendency which they show to 

 pass through spontaneous and cyclical changes. 



To sum up, all bodies which are composed of an aggrega- 

 tion of diverse but definitely related parts, which have a defi- 

 nite shape, bounded by curved lines and presenting concave 

 and convex surfaces, which increase in size by the intussus- 

 ception of foreign particles, and which pass through certain 

 cyclical changes, are organised; and it is with the study of 

 bodies such as these that Biology is concerned. 



In the foregoing it has been assumed, for the sake of simpli- 

 city, that all living bodies exhibit organisation. It is to be 

 remembered, however, that there are living bodies {e.g., Fora- 

 minifera) to which the term of "organised," as above defined, 

 cannot be applied. Such bodies are living, but they are not 

 organised. In these cases the distinction from dead matter de- 

 pends wholly upon the mode of growth, and upon the presence 

 of vital activity as shown by the occurrence of various periodic 

 changes. 



The grand and fundamental characters by which living 

 bodies are distinguished from dead bodies are these: — i. Every 

 living body possesses the power of taking into its interior cer- 

 tain foreign materials, and converting these into the substances 

 required to build up fresh tissue or repair waste. By this 

 power of "assimilation," as it is called, a living hoAy groivs. 



2. Living bodies, as they are constantly assimilating fresh mat- 

 ter, are incessantly losing portions of their substance — or, in 

 other words, partial death is a constant accompaniment of life. 



3. If our observation be continued for a sufficient length of 

 time, we find that every living body has the power of repro- 

 ducing its like. That is to say, every living body has, directly ■ 

 or indirectly, the power of giving origin to minute germs which 

 are developed into the likeness of the parent. 4. The matter 

 of a living body is subject to the same physical and chemical 

 forces as those which affect dead matter; but it is further the 



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