Lessons on Soil

by Edward J. Russell

Fig. 26. Soils contain tiny things that grow on gelatine

Another experiment is easy but takes a little longer to show. Mix two sheets of leaf gelatine with a quarter of a pint of boiling water, pour into each of three saucers, and cover over with plates. Then stir up some baked soil in a cup half full of cold boiled water, and quickly put a teaspoonful of the liquid into a second cup, also half full of cold boiled water. Stir quickly and put a spoonful on to the jelly, tilting it about so that it covers the whole surface and label the saucer "baked soil." Do the same with the "unbaked soil," labelling the saucer; leave the third jelly alone and label it "untouched." Cover all three with plates and leave in a warm place. After a day or so little specks begin to appear on the jelly containing the unbaked soil, but not on the others (Fig. 26); they grow larger, and before long they change the jelly to a liquid. The other jellies show very few specks and are little altered. These creatures making the specks came from the soil because so few are found on the jelly alone; they were killed in the baking and so do not occur on the baked soil jelly.