LIFE. 3 



given above ; many forms of fresh-water algae, common in 

 our ponds and ditches, are sealed up in ice during the 

 winter, and on the return of spring at once resume the 

 active condition. In relation to pressure we find an equal 

 range, life extending from an altitude of 20,000 feet above 

 the sea-level, and down to as far below that point. Finally, 

 relating to moisture, some of our common fresh-water alga 

 that flourish in water or in damp situations retain their vitality 

 after being blown about as dry dust for a considerable length 

 of time. The above remarks illustrate the extremes under 

 which life in the broader sense can exist, but it must be 

 remembered that the range of life of any one kind of 

 organism is usually restricted within much narrower limits 

 in relation to all forces acting on it. As a rule, the lower 

 the organism stands in the scale of development, the greater 

 its power of successfully overcoming extremes. The above- 

 mentioned property of protoplasm in being capable of 

 passing from the active to the passive condition, which 

 means the power of acting differently under different 

 conditions of environment, is not unique, but may be com- 

 pared with the behaviour of iron under different conditions : 

 at ordinary temperatures iron is a good conductor of elec- 

 tricity, but when heated to a certain temperature, this 

 peculiar property ceases, yet the chemical condition of 

 the iron is unchanged at the higher temperature, conse- 

 quently its different behaviour is attributed to a physical 

 change induced by surroundings ; so with protoplasm. 



From amongst the several characteristics of Uving matter, 

 the two following may be considered as typical and universal. 



(i) Growth. — All living organisms agree in growing or 

 increasing in size, more especially during the early period 

 of their existence, and the peculiar manner in which this is 



