"The treatise has now been seven years before the public, has been most acutely investigated by those best competent to test its value, and the first physiologists of our day have judged the discoveries which it unfolds as worthy to be ranked amongst the most important steps by which the science of physiology has ever been advanced"
The treatise being described here is Theodor Schwann's work of 1837, Mikroskopische Untersuchungen über die Uebereinstimmung in der Struktur und dem Wachsthum der Thiere und Pflanzen. This was translated into English in 1847 as Microscopical researches into the accordance in the structure and growth of animals and plants (the quote above comes from the Translator's Preface). But to summarise Schwann's achievements, let's just use two words: cell theory.
Schwann - who was born 200 years ago today - played a key role in our understanding that cells are the basic units of life. Schwann's associate Matthias Schleiden had examined the cellular structure of plants, but Schwann extended Schleiden's research to animal tissues. As the title of Section II of Schwann's Microscopical researches... states: "On cells as the Basis of All Tissues of the Animal Body".
Schwann's work was aided by developments in nineteenth century microscopy. Microscopical researches... includes a number of plates with figures of the cells Schwann observed under his microscope (magnified by about 450 diameters). Here were membranes from a hen's egg and cells from the tail of a tadpole, not served up as remarkable feats of magnification but as evidence to support his theory.
Aided by being part of the laboratory of the influential German physiologist Johannes Muller, Schwann's monograph caught the attention of the scientific community and he was awarded the Royal Society's Copley Medal in 1845 (two years before his work was published in English).
Although Schwann's theory was refined in later years (Rudolf Virchow showed that cells developed from themselves, rather than as Schwann argued, crystallizing out from a "blastema" or amorphous fluid) he played a vital role in the adoption and acceptance of cell theory. Considering also Schwann's earlier research - he made pioneering discoveries in both fermentation and digestion - the bicentenary of his birth seems an apt date to mark.