1. All living things are made of cells.
2. Cells are the basic units of life.
3. Living cells only come from other living cells.

• 334 B.C.E.
• Aristotle observed nature directly.
• He classified all known organisms as either plants or animals.
• B.C.E.= Before Common Era

• The first microscope!
– Zacharias and Hans
Jansen
– 1595
– Middleburg, Holland
– Placed two lenses in a tube

Hans & Zacharias
Janssen
• 1595
• Hans & Zacharias Janssen produced the first compound microscope by lining up 2 lenses.

• 1665
• Robert Hooke observed lining matter (cork cells) through a compound microscope, which reveals empty cells.
• He is the first to call the spaces in the cork “cells” which means little rooms.

Anton van
Leeuwenhoek
• 1675
• Anton van Leeuwenhoek observed living bacteria and blood cells through a simple microscope.

• 1838
• Matthias Schleiden discovered that plants were made of cells.
• He believed plant growth happened through the production of new cells

• 1839
• Theodor Schwann states “all animals are made of cells.”
• Believed plant and animal cells were different in structure, but the cell was the basic unit for life.

William Henry Perkin
• 1856
• William Henry Perkin develops an intense purple dye, which is used to stain slides.

• 1858
• Rudolph Virchow states…
– “Cells are the last link in a great chain that forms tissues, organs, systems, and individuals. Where a cell exists, there must have been a preexisting cell.”
• Cells can only arise from pre-existing cells
• He also stated that diseases caused changes in a normal cell