6 INTKOriUCTUlX. 



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

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

 toplasm, if free to do so, lias the ])o\ver of throwing out processes 

 of its own sulistance, 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 < it its own substance which laav become developed 

 into fresh masses of protojilasm. 



Ill some cases, though proto])lasm lie 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- 

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

 dormant into one. of (tctirc life. 



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

 conditions to be j)resent before any external vital jihenoniena can 

 be maiiife.sted ; and usually life itself, even in a dormant state, can- 

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

 presence of atnios|iheric air (or rather of free oxj'geu) is in an ordi- 

 nary way essential to active life. The higher manifestations of 

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

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

 Fahr. AVater, again, is an essential constituent of protojilasm in its 

 living state, aiul is therefore absolntel}' essential to the carrying on 

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

 or plant will in most Ciuses kill it outright, and will always suspend 

 all visible vital jihenoniena. 



Lastly', the great majority of living beings are organised — tliat is 

 to say, they are composed of ditlereiit parts, or organs, which hold 

 certain relations with f)iie another, and which discharge different 

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

 .lari/ accompaiiiment of vitalitj-, 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 ne\-ertheless discharge all their vital functions just as well as 

 if they possessed special organs set apart for the performance of 

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

 cause they are alive; they do not live because they are ori,'ain.sed. 



■1. ("'lassifu'ation. 



By the term cla.ssitication is understood the arraugonient of a 

 nuniliii- of dissimilar objects of any kind into laigei- or smaller 

 groujis .MTordiug as they exhibit iiioi-c ..r less likeness t w an- 



