THE CRITERIA OF LIFE 33 



without difficulty, for if warmth and moisture be sup- 

 plied the living seed begins to germinate, a plant de- 

 velops, and in the course of time new seeds identical with 

 that under observation are formed. This shows that 

 life presents various phases of activity and passivity, 

 both of which must be taken into account in biological 

 study. Unfamiliarity with the passive forms of minute 

 organisms was one of the most potent factors by which 

 belief in their spontaneous generation was kept alive. 



Life is most evident, and hence best known in its 

 active state. The passive state not infrequently escapes 

 or eludes observation so that a much broader acquaint- 

 ance with living things is necessary to appreciate it and 

 understand its significance. 



Passivity is observed among both plants and animals, 

 though among the latter it is confined to comparatively 

 few and usually to the lowest forms. It may be regarded 

 as a state in which the living organism becomes capable 

 of withstanding conditions incompatible with active 

 existence. Thus, the cold of winter, the dryness of the 

 desert, and the failure of the food supply are probable 

 factors influencing the passage of living organisms from 

 the active to the passive state, and the warmth of sum- 

 mer, the coming of rain, and the presence of food, factors 

 in bringing them once more to a state of activity. 



REFERENCE. 



THOMAS H. HUXLEY: "Anatomy of Invertebrated Animals," 

 N. Y., 1885. 



