. Biology and man. Biology; Human beings. DIAGRAM OF A CELL Under better microscopes the living stuff looks like a very fine foam full of tiny bub- bles, or like a very fine network in which tiny particles are enmeshed. It is the pro- toplasm that is the living content of the cell, and that actually builds up the cell and being adaptive. Where is the underlying sameness? It was impossible to answer this until the microscope had been improved to a certain point. In the seventeenth century it was already possible to find hundreds of living things that are too small for the human eye to see unaid
. Biology and man. Biology; Human beings. DIAGRAM OF A CELL Under better microscopes the living stuff looks like a very fine foam full of tiny bub- bles, or like a very fine network in which tiny particles are enmeshed. It is the pro- toplasm that is the living content of the cell, and that actually builds up the cell and being adaptive. Where is the underlying sameness? It was impossible to answer this until the microscope had been improved to a certain point. In the seventeenth century it was already possible to find hundreds of living things that are too small for the human eye to see unaided. A Dutch merchant, Anton van Leeuwenhoek (1632-1723), and an English contem- porary, Robert Hooke (1635-1703), made their own microscopes and peered at all kinds of very small objects. In a thin slice of cork Hooke saw little compartments to which he gave the name cells, or chambers, since they reminded him of the cells of a beehive—or a monastery (see illustra- tion, p. 21). Subsequently hundreds of students saw that all the plants and animals that they examined consist of "cell", although these are of many sizes and shapes. In 1839 a German botanist, Matthias Schleiden (1804-1881), and his friend Theodor Schwann (1810-1832), a zoologist, developed the idea that the "cell" is the "unit of structure" in all living things (see illustration, p. 21). They were not clear as to just what goes on in the cell. And they gave their attention mostly to the walls or membranes of the cells. But using the cell idea led to further important discoveries. Protoplasm About a hundred years ago various investigators in France, Italy, Germany, Bohemia, and no doubt elsewhere, were searching in cells for the secret of life. They began to observe a curious slimy or jelly- like substance in both plant material and animal material—something like white-of-egg in appearance. By 1840 the Bohemian scholar Johannes Evangelista Purkinje (1787-1869) suggested the name pro
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