296 THE SCIENTIFIC MONTHLY
fied rocks, which have an estimated age of sixty million years, are be- lieved to be of bacterial origin. Sulphur bacteria similariy obtain their energy from the oxidation of hydrogen sulphide.
Bacteria thus anticipate the plant worid of algae, diatoms and carbon- formers, as well as the animal worid of protozoa and mollusca, by play- ing an important role in the formation of the new crust of the earth. This is obsen^ed in the primordial limestone depositions composed of calcium carbonate formed by bacterial action on the various soluble salts of calcium present in solution in sea-water, a process exemplified to- day^* in the Great Bahama Banks where chalk mud is now precipitated through accumulation by B, edicts. Doubtless in the shallow conti- nental seas of tlie primal earth such bacteria swarmed, as in the shallow coastal seas of to-day, having both the power of secreting and precipi- tating lime and, at the same time, of converting nitrogen combinatioiis. In the warm oceanic waters the amount of lime deposited is largei and the variety of living forms is greater ; but the number of living forms which depend for food on the algae is less because the denitrifyiiig bac- teria which flourish in warm tropical waters deprive the algae of the nitrates so necessary for their development. Again, where algal ^^rowth is scarce, the protozoic unicellular and multicellular life (plankton) of the sea, which lives upon the algae, is also less abundant. This affords an excellent illustration of the great law of the balance of the life environment through the equilibrium of supply of energy, one aspect of the interaction of organisms with their life-environment. The denit- rifying bacteria rob the waters of the energy needed for the lowest forms of plants, and these in turn are not available for the lowest terms of animal life. Thus in the colder waters of the oceans, where the denitrifying bacteria do not exist, the number of living forms is far greater, although their variety is far less.**
The so-called luminous bacteria also anticipate the plants and ani- mals in light production,*® which is believed to be connected with the oxidation of a phosphorescing substance in the presence of water and of free oxygen.
The parasitic life of bacteria began with their symbiotic Telations with other bacteria, and was extended into intimate relations with the entire living world. The number of these organisms is inconceivable. In the daily excretion of a normal adult human being it is estima^fti that there are from 128 billion to 33 trillion bacteria, which 'woiAi weigh approximately 5 5/10 grams when dried, and that the nitrogen in this dried mass would be about 0.6 gram, constituting nearly one half the total intestinal nitrogen.*^
14 Drew, George IL, 1914, p. 44.
15 Pirsson, Louis V., and Schuchert, Charles, 1915, p. 104.
16 Harvey, E. Newton, 1915, pp. 230, 238.
17 Kendall, A. I., 1915, p. 209.
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