SUMMARY AND REVIEW. 



dom is necessary to the vegetable kingdom and 

 vice versa, the plant and vegetable world giving 

 off oxygen for use of the animal world, and the 

 animal world in its turn supplying the plant 

 and vegetable world with carbon dioxide in a 

 ceaseless round. All other foods used to sus- 

 tain animal and plant life are so arranged by 

 the processes of Nature as to be used again and pood Supply, 

 again in a cbntinuous circle, first by plants and 

 then by animals, and then over again by plants, 

 the circle to endure so long as the sun shines 

 and the rain falls to, promote its continuance. 

 Many of these processes require much thought 

 in order to understand the intricate workings 

 of Nature. Those who undertak-e the study in 

 earnest find it of special interest. Not the least 

 interesting phase is the way in which nitro- 

 genous foods, so necessary to animal life, take 

 their place in the continuous circle, and how, 

 through the assistance of bacteria they are 

 prepared to return to take part in the main- 

 tenance of plant and vegetable life. 



Bacteria which assist in the sprouting of 

 seeds and in other processes of Nature in farm 

 and garden, form an interesting study, also. 



SUMMARY OF CHAPTER II. 



Mysteries with regard to diseases revealed by 

 the microscope. 



35 



