Frequency of bowel movements varies widely among individuals, as well as varying widely for any single individual. In studies on the subject, approximately 50 to 70 percent of people surveyed report having a single daily bowel movement. Outliers range from one movement every three days to three movements a day.
Cell theory was eventually formulated in 1839. This is usually credited to Matthias Schleiden and Theodor Schwann. However, many other scientists like Rudolf Virchow contributed to the theory. The three tenets to the cell theory are as described below: All living organisms are composed of one or more cells.
The word cell was first used by English scientist Robert Hooke in 1665 to describe the cell walls visible in cork when seen through a microscope. In 1838 the German botanist Mâ¦atthias Schleiden concluded that all plant tissues were made of cells. In 1839 the zoologist Theodor Schwann reached the same conclusion about animal tissues. By 1885 the German physiologist concluded that cells only originated by the division of a preexisting cell.