To observe these strange little creatures it is only necessary to squeeze some of the white congealed perspiration from one of these glands on to a slide, coyer it with a drop of oil or xylol and spread out the object with a needle. By cutting down the light considerably by means of the diaphragm, we shall be able to distinguish all the stages of these little creatures which, unbidden, share our lives.
Other parasites come to us in our food and, of these, one of the most dangerous is known as Trichinella Spiralis and gives rise to a disease known as trichinosis. We need not give a precise account of the life history of this interesting worm, it will suffice for our purpose to know that it finds its way into the bodies of human beings, in badly cooked pork or in improperly cured ham or bacon. The little worm is only about 1/25 inch long and, at first, dwells in the intestines of the pig. Each female produces upwards of fifteen thousand young and these pass into the blood of their host and thence to its muscles. Snugly coiled into a spiral between the muscle fibres, each young worm becomes surrounded with a lemon-shaped covering, which is exceedingly resistant. Suppose now a human being should happen to eat such pork, the juices of the stomach would dissolve the pork and also the little case enclosing the parasite. Once set free in the human body, the whole proceeding is repeated and, at last, the result is very severe muscular pains for the victim. The medical man is called upon to study such parasites as Trichinella, and they are not so uncommon as one might think.
In addition to animal parasites medical science demands a knowledge of many disease bringing fungi. One of the commonest is the fungus responsible for the unpleasant malady called ringworm. But we have written sufficient to show that the general practitioner needs his microscope always by his side. Not only so but very many instruments he uses in his work, though called by other names, are really microscopes adapted for special purposes.
CHAPTER XIII
THE MICROSCOPE AND AGRICULTURE
Probably there are not many farmers who use a microscope and fewer still who use one to help them in their business, yet there are few people to whom one of these instruments would be more useful. Their seeds are often far from pure and the microscope will reveal the impurities which may consist of dirt and dust, or of other seeds, seeds which will grow into weeds and make the crop less valuable or, if present in large quantities, render it valueless. Agricultural plants become attacked by varied diseases which can only be studied under the microscope; insects also do their share of destruction and much may be learned about them when they are magnified. Fungi and insects not only attack crops but domestic animals as well. The microscope is an invaluable aid in studying the soil, in dairy work and in many other ways closely connected with agriculture.
That the testing of agricultural seeds is very important is shown by the fact that not very long ago a deputation urged the Government to establish a National Seed Testing Station; no further plans have been made, however. Seed testing is very interesting work, every seed has its particular shape and markings and the student soon becomes absorbed in seeking for weed seeds among the collections he examines. A weed in the sense we use it here is not necessarily a harmful plant, it is a plant in the wrong place. For example a carrot growing in a field of turnips, though a useful plant would be a weed. When the farmer sowed turnip seed he did not do so with the object of raising carrots.
The only apparatus necessary for the study of most farm seeds is a powerful magnifying glass, one that will enlarge the seeds ten diameters or more. When beginning this work, a difficulty occurs at once for, without assistance from an expert, it is by no means easy to learn the names of the seeds one examines. The difficulty can be overcome to a certain extent if we know the names of flowers, for then we can collect the seeds from these flowers and we shall have properly named specimens as a guide. Beginning in this way, we shall soon find that the seeds can be arranged in groups and there will then be no difficulty in recognising say clover seed or grass seed, though much more experience will be necessary before we can say to which kind of clover or grass the seed belongs.
Many of these seeds are well worth studying, whether we are interested in seed testing or not. The corn buttercup and the wild carrot have curious spined seeds; those of the larkspur when magnified appear to be studded with little shreds of paper. White and red campion, have kidney shaped seeds studded with warts and so similar to one another that the microscopist who can distinguish one from the other may consider himself something of an expert. Spurrey has lens shaped seeds with raised equator-like rims. Evening primrose seeds are curious because they are found in all sorts of shapes. The seeds of rib-wort plantain resemble miniature date seeds, others resemble minute bananas, some are perfectly round, others almost square; some have smooth shining surfaces which look as though they had been artificially polished, others again are wrinkled and deeply furrowed; but, most curious of all the common seeds are those of the cornflower, they resemble nothing so much as little shaving-brushes, with bright yellow bristles. Many profitable hours may be spent in studying the seeds of our common native plants, both wild and cultivated.