CHAPTER III. 

 THE VITAL PKOPEETIES OF THE CELL. 



I. The Phenomena of Movement. All the mysteries of 

 life, which are exhibited by plants and animals, are present, as it 

 were in a rudimentary form, in the simple cell. Each individual 

 cell, like the whole complex organism, has an independent life of 

 its own. If we wish to study more deeply the true nature of 

 protoplasm, we must above all things investigate its most important 

 properties, its so-called vital properties. However, life, even the 

 life of the simplest elementary organism, is a most complex 

 phenomenon, which it is most difficult to define ; it manifests 

 itself, to use a wide generalisation, in this, that the cell in conse- 

 quence of its own organisation, and under the influence of its 

 environment, experiences continual changes and develops powers, 

 by means of which its organic substance is being continually 

 broken down and built up again. During the former process, 

 energy is set free. The whole vital process, as Claude Bernard 

 (IV. IA) expresses it, depends upon the continual co-relation of 

 this organic destruction and restoration. 



It is most convenient to classify these most complex phenomena 

 under four heads. Thus each living organism exhibits four 

 different fundamental functions or properties, by .means of which 

 its life is made manifest : it can alter its form, and exhibit move- 

 ments ; it reacts to certain external stimuli in various ways, that 

 is to say, it is irritable ; it has the power of nourishing itself, it 

 can by absorbing and transforming food material, and by giving 

 up waste products, form substances, which it utilises for growth, 

 for building up tissues, and for special vital functions ; finally, it 

 can reproduce itself. 



Hence we will discuss the vital properties of the cell in four 

 chapters, which we will take in the following order : 



1. Phenomena of movement. 



2. Phenomena of irritability. 



3. Metabolism and formative activity. 



4. Reproduction. 



