b INTEODUCTION. 



boiled. In its living state also, protoplasm appears invariably to 

 have the power of movement. Thus, any little mass of living pro- 

 toplasm, if free to do so, has the power of throwing out processes 

 of its own substance, and thus of moving and changing its place. 

 It has, also, the power of increasing in size or of maintaining its 

 existence by " assimilating " fresh and foreign material ; and it may 

 detach portions of its own substance which may become developed 

 into fresh masses of pi'otoplasm. 



In some cases, though protoplasm be present, there is no external 

 and visible manifestation of life, as is the case with eggs and seeds, 

 which exhibit what is called a " dormant " vitality. This condition 

 may remain for a long time unchanged, until the external circum- 

 Jstances are altered, and then the organism passes from a state of 

 dormant into one of active life. 



As a general rule, therefore, it is necessary for certain external 

 conditions to be present before any external vital phenomena can 

 be manifested ; and usually life itself, even in a dormant state, can- 

 not be maintained in the absence of these conditions. Thus, the 

 presence of atmos]3heric air (or rather of free oxygen) is in an ordi- 

 nary way essential to active life. The higher manifestations of 

 vitality, again, are only possible between certain limited ranges of 

 temperature, varying from near the freezing - point to about 120° 

 Fahr. Water, again, is an essential constituent of protoplasm in its 

 living state, and is therefore absolutely essential to the carrying on 

 of vital processes of all kinds. Hence the mere drying of an animal 

 or plant will in moat cases kill it outright, and will always suspend 

 all visible vital phenomena. 



Lastly,'the great majority of living beings are organised\-\)a?X is 

 to say, they are composed of different jKirts, or organs, wmch hold 

 certain relations with one another, and which discharge different 

 functions. It is not the case, however, that organisation is a neces- 

 sary accompaniment of vitality, or that all living beings are organ- 

 ised. Many of the lower forms of life exhibit absolutely no visible 

 structure, and cannot, therefore, be said to be " organised " ; but 

 they nevertheless discharge all their vital functions just as well as 

 if they possessed special organs set apart for the performance of 

 each. Animals, therefore, are orgaiiised, or possess structure, be- 

 cause they are alive ; they do not live because they are organised. 



4. Classification. 



By the term classification is understood the arrangement of a 

 number of dissimilar objects of any kind into larger or smaller 

 groups according as they exhibit more or less likeness to one an- 



