Delphinidin

Imagine the excitement of the first scientist who observed cells! This discovery was made in 1665 by the English physicist Robert Hooke, who used a primitive microscope to examine thin slices of cork found in stoppered wine bottles:

I took a good clear piece of Cork, and with a Penknife sharpen’d as keen as Razor, I cut a piece of it off, and thereby left the surface of it exceedingly smooth, then examining it very diligently with a microscope, methought I could perceive it to appear a little porous . . . these pores, or cells . . . were indeed the first microscopical pores I ever saw, and perhaps that were ever seen, for I had not met with any Writer or Person, that had made mention of them before this . . . I had with the discovery of them, presently hinted to me the true and intelligible reason of all the Phaenomena of Cork.

Hooke compared the boxlike compartments he saw to the surface of a honeycomb and is credited with applying the term cell to those compartments. He also estimated that a cubic inch of cork would contain approximately 1,259 million such cells. What Hooke saw in the cork were really only the walls of dead cells, but he also saw “juices” in living cells of elderberry plants and thought he had found something similar to the veins and arteries of animals.

Two physicians, Marcello Malpighi in Italy and Hooke’s compatriot Nehemiah Grew in England, along with Anton van Leeuwenhoek, reported for 50 years on the organization of cells in a variety of plant tissues. In the 1670s, they also reported on the form and structure of single-celled organisms, which they referred to as “animalcules.”

After this period, little more was reported on cells until the early 1800s. This lack of progress was mainly due to imperfections in the primitive microscopes and the crude way in which tissues were prepared for microscopic examination. Microscopes and tissue preparations both slowly improved, however, and by 1809, the famous French biologist Jean Baptiste de Lamarck had seen a wide enough variety of cells and tissues to conclude that “no body can have life if its constituent parts are not cellular tissue or are not formed by cellular tissue.” In 1824, René J. H. Dutrochet, also of France, reinforced Lamarck’s conclusions that all animal and plant tissues are composed of cells of various kinds. Neither of them, however, realized that each cell could, in many cases, reproduce itself and exist independently.

In 1831, the English botanist Robert Brown discovered that all cells contain a relatively large body that he called the nucleus. Soon after the discovery of the nucleus, the German botanist Matthias Schleiden observed a smaller body within the nucleus that he called the nucleolus. Schleiden and German zoologist Theodor Schwann were not the first to understand the significance of cells, but they explained them more clearly and with greater insight than others before them had done. They are generally credited with developing the cell theory, beginning with their publications of 1838 to 1839. This theory, in essence, states that all living organisms are composed of cells and that cells form a unifying structural basis of organization.

In 1858, another German scientist, Rudolf Virchow, argued persuasively in a classic textbook that every cell comes from a preexisting cell (“omnis cellula e cellula”) and that there is no spontaneous generation of cells. Virchow’s publication stirred up much controversy because there had previously been a widespread belief among scientists and nonscientists alike that animals could originate spontaneously from dust. Many who had microscopes were thoroughly convinced they could see “animalcules” appearing in
decomposing substances.

The controversy became so heated that in 1860, the Paris Academy of Sciences offered a prize to anyone who could experimentally prove or disprove spontaneous generation. Just 2 years later, the brilliant scientist Louis Pasteur of France was awarded the prize. Pasteur, using swannecked flasks, demonstrated convincingly that boiled media remained sterile indefinitely if microorganisms from the air were excluded from the media.

In 1871, Pasteur proved that natural alcoholic fermentation always involves the activity of yeast cells. In 1897, the German scientist Eduard Buchner accidentally discovered that the yeast cells did not need to be alive for fermentation to occur. He found that extracts from the yeast cells would convert sugar to alcohol. This discovery was a big surprise to the biologists of the time and quickly led to the identification and description of enzymes , the organic catalysts (substances that aid chemical reactions without themselves being changed) found in all living cells. This also led to the belief that cells were little more than miniature packets of enzymes.

During the first half of the 20th century, however, further advances were made in the refinement of microscopes and in tissue preparation techniques. Many structures and bodies, besides the nucleus, were observed in cells, and the relationship between structure and function came to be realized and understood on a much broader scale than previously had been possible.