He carefully studied the structure of a garden spider, and for the first time explained its wonderful feet, its jaws and poison gland, its spinnerets and silk. He studied Hydra first of all men, and said that, under the microscope, its tentacles appeared to be several fathoms long. Although sadly at sea over the correct position of his snails in the animal world, he was clever enough to include Volvox amongst the plants and fortunate enough to see the young forms escape from the parent colony.
Concerning this microscopist’s early studies in bacteriology we may quote from Professor Miall’s The Early Naturalists, a book by the way of the greatest interest to those who would learn something of the struggles of the men who laid the foundations of our present-day biological knowledge.
Professor Miall says: “In 1683 Leeuwenhoek wrote a letter to the Royal Society which contains the first mention of bacteria. He had been writing and speculating upon saliva, and had searched the saliva of the human mouth for animalcules without finding any. It then occurred to him to ask whether the teeth might lodge animalcules discharged from the salivary ducts. He tells us that, though his own teeth were scrupulously clean and particularly sound for his age (about fifty), the lens revealed a white deposit upon them. This deposit was found to contain minute rods, some of which showed either a steady or gyratory movement. Others were very minute, of rounded form, and moved with remarkable velocity. The largest of all, which were either straight or bent were motionless. The teeth of an old man, which were never cleansed, contained among others large rods which exhibited snake-like undulations. Rubbing the teeth with strong vinegar did not kill the moving bodies, but they became quiescent when detached and placed in a mixture of vinegar and saliva, or vinegar and water. Nine years later Leeuwenhoek returned to the subject. Living particles were no longer met with in his teeth, and he was at a loss to explain why, until it occurred to him that he was accustomed to drink hot coffee every morning. This, he thought might have killed the animalcules, and his conclusion was confirmed by finding that on the back teeth, which were less exposed to the hot drink, plenty of them were still to be found. In 1697 he tells how he pulled out a decayed tooth, and found that the cavity abounded in moving particles.” Nearly a hundred years elapsed before anyone else took up the study of bacteria.
From the time of Leeuwenhoek onwards, scientific discoveries were announced in rapid succession, so that in one short chapter it is impossible to keep pace with the progress that was made. Among the great men who owe much of their success to the microscope we may mention the Frenchman Réaumur, whose memory is kept green for all time by his thermometer; as a worker upon problems of insect life he was indefatigable; the Swede, Linnæus, to whose early efforts we owe the orderly arrangement of living creatures and plants, known as classification. This arrangement has been considerably modified, more modern ideas have upset much that he initiated, yet he remains the parent of orderly arrangement.
Buffon, a great naturalist, was followed by Cuvier, the first serious student of fossils; by Humboldt, naturalist and traveller; by Robert Brown, the founder of modern Botany; by Darwin and by Pasteur in turn. How much these men owe to the microscope can never be known; certain it is that without its assistance our world, the world we know and can see, would have been smaller than it is to-day.
CHAPTER III
THE ACTION OF LIGHT
It is hardly necessary to remark that the wonderful properties of the microscope depend upon light. Without light, lenses would be useless, objects could not be illuminated and we could not see them. In this short chapter we propose to give a brief outline of the action of light; if our words appear to savour of the school-book, we shall try to avoid it, but, we repeat, if they do so we would remind our readers that the more one knows of the action of light the better use one can make of one’s instrument. As a well-known microscopist has remarked we may be able to afford a costly harp or a costly microscope, but although we may be able to strike a few notes on the former and examine a few objects with the latter, we can only make the best use of either by thoroughly understanding and practising upon it.
The first thing we learn when we study light is that it travels in straight lines. The chief source of light to the inhabitants of this earth is the sun. Now the sun is so far away that, for all practical purposes, the rays of light coming from it may be looked upon as being parallel to one another. That we must always remember, when dealing with the sun, though, of course, it does not apply when we are dealing with lights near at hand, unless they are specially constructed to throw parallel beams or rays, whichever we elect to call them. To prove that light travels in straight lines is not difficult, and we may devise a number of experiments for the purpose. The doors and ventilators of many dark rooms, in which photographic operations are carried on, are constructed on the assumption that light cannot travel round corners. An arrangement as shown in the diagram will allow air, but no light, to pass. If light were capable of going round corners, some other arrangement would have to be devised for the ventilation of dark rooms.