CHAPTER IV. 



THE VITAL CHARACTERS OF ORGANISMS. 



The manifestation of so-called vital phenomena in man forms 

 the subject-matter of the following chapters, and some kind of 

 explanatory definition of the vital characters of the simpler 

 organisms will be useful in preparing the beginner's mind for the 

 more intricate questions in human physiology. This, with the 

 foregoing short account of the chemical and structural peculiari- 

 ties of animals, will complete a rough outline of the general char- 

 acter of organisms. 



Protoplasm has already been referred to as the material capable 

 of showing " vital phenomena," the most obvious and striking of 

 which are its movements. 



Besides the common molecular or Brownian movement of the 

 granules of protoplasm which may be seen in most cases where 

 fine granules are suspended in a less dense medium protoplasm 

 can perform motions of different kinds which must be regarded 

 as distinctly vital in character. This movement may be said to 

 be of three different kinds, according to the results produced, 

 viz. : (1) The production of internal currents. (2) Changes in 

 form. (3) Locomotion. In reality, the two latter are dependent 

 on the first. 



The occurrence of currents from one part of a portion of proto- 

 plasm to another can be well seen in vegetable cells, when the 

 cell wall restricts the more obvious change in form or place. Thus 

 in the cells forming the hair on the stamens Tradescantia Vir- 

 ginica the various currents can be seen in the layers of protoplasm 

 which line the cell wall. 



The granular particles course along in varying but definite 

 directions, passing one another like foot passengers in a crowded 

 street. The first and most obvious result of this is, that the vari- 

 ous parts of the substance are constantly brought into contact with 

 one another, and thus the products of any chemical changes 



83 



