(5) But they have first to undergo some change, and the agent producing this change is more active in the top soil than in the subsoil. (6) The top soil is much the most useful part of the soil and should never be buried during digging or trenching, but always carefully kept on top. {53} CHAPTER VII THE DWELLERS IN THE SOIL Apparatus required. _Garden soil. Six bottles and corks [1]. Twelve Erlenmeyer flasks, 50 c.c. capacity [2]. Cotton wool. Milk (about half a pint). Leaf gelatine. Soil baked in an oven. Six saucers [3]. The apparatus in Fig. 28 (two lots). Wash bottle containing lime water (Fig. 27, also p. 19)._ In digging a garden a number of little animals are found, such as earthworms, beetles, ants, centipedes, millipedes and others. There are also some very curious forms of vegetable life. By carefully looking about it is not difficult to find patches of soil covered with a greenish slimy growth; they are found best under bushes where the soil is not disturbed, or else where the soil has been pressed down by a footmark and not touched since. Any good soil left undisturbed for a time shows this growth. Put some fresh moist garden soil into a bottle and cork it up tightly so that it keeps moist. Write the date on the bottle and then leave it in the light where you can easily see it. After a time--sometimes a long, sometimes a shorter time--the soil becomes covered with a slimy growth, greenish in colour, mingled here and there with reddish brown. The longer the {54} soil is left the better. Often after several months something further happens; little ferns begin to grow and they live a very long time indeed. There is at Rothamsted a bottle of soil that was put up just like this as far back as 1874. For a number of years past a beautiful fern has been growing inside the bottle, and even now it is very healthy and vigorous. If, instead of being kept moist, the rich garden soil is left in a dry shed during the whole of the winter so that it gradually loses its moisture, it will generally show quite a lot of white fluffy growth. All of these living things are very wonderful, and some, especially earthworms, are very useful to gardeners and farmers.