The Invention of the Microscope

views updated

The Invention of the Microscope

Overview

Historical records indicate that around the time of Christ the ancient Assyrians first realized that glass spheres could be used as magnifying devices. Claudius Ptolemy, a second-century mathematician and astronomer in Alexandria, wrote a paper on the optical properties of lenses. He discussed how glass spheres filled with water could be used for magnification and refraction. However, despite this knowledge, glass lenses were not extensively used for over a millennium. Around 1300, spectacles were invented to improve vision. This innovation served as the springboard to strong interest and research into the properties of magnifying lenses. Several treatises were published in the sixteenth century as a result. Near the end of the sixteenth century, it was found that if certain lenses were joined together by a cylinder, they would become what is called either a Galilean telescope or a Galilean microscope, depending on which end is used to view objects. Italian mathematician and astronomer Galileo (1564-1642) used this device as a telescope to observe the stars and planets but did little to advance its use as a microscope for biological purposes.

The earliest simple microscopes (containing only a single lens) used drops of water confined to a small hole that functioned as a magnifying lens. Eventually glass replaced water as the medium, but it is not clear when glass lenses first began to be used. It has been well established that by the seventeenth century Antoni van Leeuwenhoek, a Dutch scientist, had developed techniques for making high-quality ground lenses for simple microscopes. While these were limited in power, he used them in combination with both light and his keen eyesight to observe specimens just a few micrometers in size.

The compound microscope, which uses a multiple lens system, was first described in the sixteenth century but had little practical use at that time due to the arrangement of the lenses, the blurring of images from improper grinding, and chromatic aberrations due to problems with light. The first useful compound microscope was constructed in the Netherlands sometime between 1590 and 1608. Three different people, all of the optometrists, have been credited with the invention at one time or another: Hans Jansen, his son Zacharias Jansen, and Hans Lippershey (d. 1619?). It would be over 200 years before these problems were completely resolved, making the compound microscope an important biological tool.

Four microscopists are considered to have influenced the development and use of microscopes in biology and medicine. These individuals made significant improvements either in the technology involving microscopes or in accumulating the body of knowledge of microscopic structure. They were Marcello Malpighi (1628-1694), Anton van Leeuwenhoek (1632-1723), Jan Swammerdam (1637-1680), and Robert Hooke (1635-1703).

Background

Marcello Malpighi was an Italian biologist and physician who conducted extensive studies in animal anatomy. He was one of the first scientists to use a microscope to study the structure, composition, and function of tissues, so he is often known as the father of histology (the microscopic study of tissues). Among his many accomplishments dealing with the human body was the first description of capillaries, the inner layer (dermis) of the skin, the papillae of the tongue, the outer portion of the brain (cerebral cortex), and red blood cells. He wrote detailed treatises on animals and insects, including descriptions of the development of the chick embryo and the lifecycle of the silkworm, and demonstrated that pests such as the flea and weevil reproduce through ordinary insect means and not by spontaneous generation (the concept that living organisms could be created from nonliving matter). In addition, Malpighi made detailed investigations into plant anatomy. He systematically described the various parts of plants, such as bark, stem, roots, and seeds, and discussed such processes as germination (the beginning of growth). Although Malpighi did little to expand the technical aspect of microscopes, he did have a significant impact on the advancement of the body of knowledge in biology.

Anton van Leeuwenhoek, a Dutchman who spent most of his life in Delft, sold cloth for a living. Although he had little formal schooling, as a young man he became interested in making magnifying lenses and recording his observations. This soon became an obsession. Leeuwenhoek used a small single-lens system and achieved magnifications that allowed him to see in much greater detail than was allowed by any microscope of the time. Unfortunately, Leeuwenhoek closely guarded his lens-making technique, so his improvements died with him. Although he was not willing to share his methods, Leeuwenhoek was more than willing to share his observations. In fact, he became somewhat of a celebrity because of his publications regarding his research. He is most famous for his discovery of animalcules (one-celled animals, now known as protozoa) in stagnant water, which he reported in the mid-1670s. He made significant contributions in the areas of capillaries, the structure of muscle, the lens of the eye, the reproductive system, and teeth. He studied bacteria from the mouth and recognized the various shapes, postulating correctly on their relative size to red blood cells.

Jan Swammerdam was a contemporary and countryman of Leeuwenhoek. In contrast to Leeuwenhoek, Swammerdam was a well educated and highly systematic scientist who confined his attention to studying relatively few organisms in great detail. He was responsible for many highly innovative techniques, such as injecting wax into objects to hold them firm, dissecting fragile objects under water, and using micropipettes to inject organisms under the microscope. Swammerdam concentrated his research on what he considered to be insects based on their mode of development. These included such organisms as spiders, snails, scorpions, fishes, and worms. Unfortunately, Swammerdam was subject to fits of mental instability and had financial difficulties that led to periods of depression. He died at the early age of 43, having contributed a significant amount of research to biology.

English physicist Robert Hooke may be the most famous of the early microscopists. He certainly had the widest array of interests. He was curator of instruments at the Royal Society of London, which allowed him to remain abreast of all new scientific developments. He made significant contributions to many areas of science and has been credited with coining the term cells while looking at cork under a microscope. In 1665 Hooke published his book Micrographia, which is primarily a review of a series of observations that he had made while following the development and improvement of the microscope. This book had tremendous influence at that time. Hooke described in detail the structure of feathers, the stinger of a bee, and the foot of the fly. He also noted similar structures to cells in the tissue of trees and plants and discerned that in some tissues the cells were filled with a liquid while in others they were empty. He therefore supposed that the function of the cells was to transport substances throughout the plant. Hooke, like the others previously mentioned, had a significant impact on biology by utilizing the microscope.

Impact

Although the work of any of the classical microscopists seems to lack a definite objective, they made significant strides by using the techniques of observation and experimentation to their fullest. It is remarkable that so few men, working independently, should have made so many fundamental observations of significant importance. Their work revealed for the first time the incredible complexity of living organisms. At the same time, it helped debunk many prevailing and unquestioned theories that had existed since the time of antiquity. The ideas of the Greek scientist Galen (a.d. 130?-200?) persisted for more than 1,000 years because they were rarely questioned, even when evidence was shown to the contrary. Thus, each of these men had to fight the preconceptions of the time and contradict prevailing wisdom to make their ideas public. They played a significant role in starting the scientific revolution.

The significance of these advances may be difficult to understand today. The microscope was relatively new, and it was not clear back then that it would ever be useful in making scientific discoveries. There was some thought that it was more of a curiosity than a scientific tool. In fact, at that time it was more a recreational device for noblemen than a tool for research. However, each of these scientists appreciated the fact that by looking at something close up, they could view things in a significantly different way. And they believed that the perspective they gained was of scientific importance. They made many important discoveries that helped to clarify some of the thinking of their time.

As an example, Malpighi made a discovery of monumental importance in physiology. William Harvey (1578-1657), a famous British physiologist, stunned the academic and medical environment with the publication of his book De motu cordis et sanguinis in animalibus (On the Motion of the Heart and Blood in Animals), in which he presented experimental and logical proof that the long-held theories of Galen were wrong. In the work Harvey proposed that blood actually travels in a circuit from the heart, around the body to the tissues, and then back to the heart. The current thinking was that blood was produced from the intestines, traveled to the liver and to the heart, and was then distributed to the body by both veins and arteries, where the tissue consumed it. Harvey's theory was a radical idea, and if it had not been for his stature, he might have been imprisoned. While some considered Harvey's idea, there was no proof that blood circulated because there was no evidence of the connection between arteries and veins. In 1660, three years after Harvey's death, Malpighi used a microscope to see the capillaries, the extremely thin blood vessels, which formed the needed connection between the arteries and veins that could not be seen with the naked eye. Other examples such as Leeuwenhoek's animalcules also raised some disquieting thoughts in the minds of his contemporaries. This helped to provide some initial evidence against the theory of spontaneous generation, held by the ancient world and passed on unquestioned up to that time. Thus, these men helped to not only provide information, but to also change the prevailing ideas of entire societies.

JAMES J. HOFFMANN