CHAPTER XVIII. 



THE CARBON, NITROGEN, SULPHUR, AND 

 PHOSPHORUS CYCLES. 



PLANTS contain ten essential elements, and these elements found 

 in the body of the plants or animals today are the same as those 

 which constituted the organic world thousands of years ago. But 

 between these dates they may have played many parts, or, in the 

 words of Duncan, "We believe we must believe in this day that 

 everything in the universe of world and stars is made of atoms, in 

 quantities x, y, or z, respectively. Men and women, mice and 

 elephants, the red belts of Jupiter and the rings of Saturn, are, one 

 and all, but ever-shifting, ever-varying swarms of atoms. Every 

 mechanical work of earth, air, fire, and water, every criminal act, 

 every human deed of love or valor; what is it all, pray, but the rela- 

 tion of one swarm of atoms to another? 



"Here, for example, is a swarm of atoms, vibrating, scintillant, 

 martial they call it a soldier and, anon, some thousands of miles 

 away upon the South African veldt, that swarm dissolves dis- 

 solves, forsooth, because of another little swarm they call it lead. 



"What a phantasmagoric dance it is, this dance of atoms! And 

 what a task for the master of the ceremonies! For, mark you, the 

 mutabilities of things. These same atoms may come together again, 

 vibrating, clustering, interlocking, combining, and there results a 

 woman, a flower, a blackbird, or a locust, as the case may be. But 

 tomorrow again the dance is ended, and the atoms are far away; 

 some of them in the fever germs that broke up the dance, others are 

 the green hair of the grave, and others are blown about the Antipodes 

 on the wings of ocean, and the eternal everchanging dance goes on.'' 



In this building up and breaking down, bacteria play an all- 

 important part. The higher plants build up the carbon and nitrogen 

 into complex organic compounds. This same end is also accom- 

 plished to a lesser degree by the animals which, however, mainly 

 act as analyzers of organic matter, but the master analysts are the 

 bacteria which are continually resolving into simple and often 

 elementary constituents, the plant and animal debris. Were this 

 not true, all the carbon and combined nitrogen of the world would 

 soon become locked up in the dead bodies of animals; plants would 

 starve and die, and animals would likewise become extinct. There- 

 fore, bacteria are the link between the living and the dead. The 



