BACTERIOLOGY. 39 



result in simpler and more important end-products. 

 These consist of the gases absolutely essential to plant 

 life, namely, carbon dioxide (CO2) and ammonia 

 (NH3). A third end-product is water (H^O). 



The amount of carbon dioxide produced by animals 

 out of starches and sugars is insignificant in comparison 

 with the needs of the vegetable kingdom, and were there 

 no other source for this important food element, the 

 plant world would either suffer a great deficit or be 

 restricted in its growth. The same is true of nitrogen, 

 another important constituent of plants, and required 

 by them in an easily assimilable form, such as ammonia 

 (NH3). It is the peculiar office of bacteria to supply 

 plants with the largest amounts of both of these constit- 

 uents. On this account they are the natural inter- 

 mediaries between plants and animals in point of food 

 production, playing by far the most important part in 

 the economy of nature. Without bacteria, plant-life 

 would be scanty or entirely wanting; and since the 

 animal kingdom depends upon plants for existence, 

 there would result a world lacking in every form of 

 higher animal life. 



The part that bacteria play as scavengers 

 Arts and of the earth and providers of food for 

 Industries, plant-life, only displays a limited side of 



their usefulness. In the arts and industries 

 they are as essential to modern economic life as are the 

 ingenious mechanical inventions of man. Many secret 



