For the most part the fossils of animal forms do not make good objects for the microscope. The Foraminifera, minute creatures dwelling in shells, are the most suitable for microscopic examination and very beautiful some of them are. They are best examined by reflected light, for then their little shells show their delicate pearly sheen.
Sponge spicules, as may be guessed from their hardness, are common in the fossil state; there are also fossils of sea-anemone ancestors and fossils also of Hydra colonies. The last named, known as graptolites, look not unlike lead-pencil marks on the rock. They exist in many forms; Diplograptus has a stem with two rows of cups in which the little creatures lived long ages ago; Monograptus has but one row of cups upon its stem, whilst Didymograptus is a branched form. These fossils are by no means rare and are worth studying under the microscope.
There are curious fossils knows as Trilobites, not unlike the present-day wood lice; they too may be studied, for some of them show all their characteristic markings as plainly as they must have appeared on the living animals.
In the plant world, many fossils in amazingly, good states of preservation have been found. Some of the giant Club Mosses from the coal measures, exhibit all the characteristic stem markings, leaf scars and the like, so clearly that one might imagine one examined a living specimen. Most of the plant remains are beyond the reach of the amateur, but many of them may be viewed in museums, in different parts of the country and the microscopist, whether he be a student of rocks or a lover of plants, should make a point of examining them. From quite fragmentary remains, scientists have been able to conjecture what vegetation covered the earth at various ages. The present is the age of flowering plants, but long ago the world was green with giant Club Mosses and Horsetails, very humble plants at the present time.
CHAPTER X
THE MICROSCOPE AS DETECTIVE
It is an unfortunate fact that our food is not always absolutely pure. It may be contaminated with foreign matter either by accident or by design. However careful the manufacturer may be in, say the preparation of cocoa, some dust, some waste vegetable matter, perhaps even a few stray dried insects may occur as impurities. They are out of place certainly but, at the worst, they are a sign of lack of care on the part of the manufacturer. There is another, more serious side to the question of food adulteration, where the foreign matter is added purposely, either because it is cheap, because it weighs heavily, imparts a pleasing colour or an agreeable aroma. Such adulteration is a form of fraud and the microscope is an invaluable aid in its detection.
In many respects the microscope is a better informant than the tests of the chemists; in some cases, however, it merely supplements and confirms the chemical results. Let us consider, for a moment, the advantages possessed by the microscope and also where chemistry scores.