Bacteria in Relation to Country Life

fur are indispensable for their development. Aside from these, they require, like the higher plants, lime, magnesia, phosphoric acid, potash and, perhaps, iron. The proportion of some of these constituents taken up by bacteria may be so slight as to preclude their recognition, even by the most refined chemical tests. Moreover, the proportions taken up are affected both by the species of bacteria and by the composition of the culture medium. Certain classes of bacteria?among them the species found in drinking-water?can develop and multiply on quantities of nitrogen compounds so minute as to be altogether insufficient for hundreds of other species. Similarly, certain groups of soil bacteria are known to require much larger quantities of lime and phosphoric acid than are required by other groups. This fact is of great significance in the struggle for existence among the bacterial inhabitants of the soil. Cell-Wall of Bacteria The cell-wall and its contents.?It is not known exactly what substance or substances enter into the composition of the cell-wall. In some cases, cellulose seems to be the main constituent. In the majority of cases, however, cellulose does not seem to be present, but, rather, a Fig. 11. Microscope and accessories for bacteriological work. horny, chitinous matter, the elements of which arc as yet unknown. Inclosed within the cell-wall is the protoplasm, a semi-fluid protein substance which is the seat of the chemical changes produc...