16 EASY LESSONS IN VEGETABLE BIOLOGY. 



extremes of heat and cold as long as the life remains. 

 There are differences in this respect in different or- 

 ganisms. The motions of some simple forms of ani- 

 mals are arrested by ice-water, and recommence on 

 increasing the temperature, but the development of 

 trout's eggs proceeds well in ice-water, while in a 

 warm room they soon die. Many kinds adapt them- 

 selves to a considerable change of temperature if it be 

 gradual. Men will endure the cold of an Arctic win- 

 ter, and, on the other hand, the workers in plaster 

 will bear for a considerable time the heat of an oven 

 raised to 500 deg. F. The influence of light, heat, and 

 electricity upon bioplasm varies according to the spe- 

 cies, some requiring a greater amount than others for 

 natural growth. As to chemical changes, the life 

 power has greater modifying power than any thing 

 else in nature. A vast variety of products in both 

 animals and vegetables are due to the controlling 

 influence of life. In a few instances the skill of a 

 chemist has imitated the product in his laboratory, 

 but the majority can only be found as the result of 

 life. Among them may be named albumen, starch, 

 sugar, and gum. Many others will occur to us as 

 we proceed in our studies.* 



* See " Science of Life," Chap. IV. 



