Lessons on Soil

by Edward J. Russell

Fig. 25. Fresh soil turns milk bad, but baked soil does not

But besides these there are some living things too small to see, that have only been found by careful experiments, but you can easily repeat some of these experiments yourselves. Divide a little rich garden soil into two parts and bake one in the kitchen oven on a patty tin. Pour a little milk into each of two small flasks, stop up with cotton wool (see Fig. 25) and boil for a few minutes very carefully so that the milk does not boil over, then allow to cool. Next carefully take out the stopper from one of the flasks and drop in a little of the baked soil, label the flask "baked soil" and put back the stopper. Into the other flask drop a little of the untouched soil and label it; leave both flasks in a warm place till the next day. Carefully open the stoppers and smell the milk: the baked soil has done nothing and the milk smells perfectly sweet; the unbaked soil, on the other hand, has made the milk bad and it smells like cheese. If you have a good microscope you can go further: look at a drop of the liquid from each flask and you find in each case the round fat globules of the milk, but the bad milk contains in addition some tiny creatures, looking like very short pins, darting in and out among the fat globules. These living things must have come from the unbaked soil or they would have been present in both flasks: they must also have been killed by baking in the oven.