The cell culture laboratory

Cultures are checked every day: the colour of the medium, and the shape and density of the cells. Mammalian cells are kept at about 37 °C, 95% humidity and 5% CO₂. The lab needs a laminar flow hood, a CO₂ incubator, an inverted microscope, an autoclave and a centrifuge.

Laminar flow hoods provide filtered, nearly sterile air to work in. Room air passes through a coarse pre-filter, then a HEPA filter, and flows smoothly over the work area.

• In a vertical (down-flow) hood, the clean air falls down onto the work and is drawn away. It is safer for the worker.
• In a horizontal (cross-flow) hood, the air blows towards the worker. It protects the cultures but gives no protection from hazardous cells.

CO₂ incubators keep the cultures sterile, at a constant temperature, with 5-10% CO₂ and about 95% humidity (so the medium does not dry out). The CO₂ cylinder is kept outside the culture room, for safety and cleanliness, and the gas is piped in.

An inverted phase-contrast microscope looks up through the bottom of flasks and dishes, where the cells grow. It shows their shape, granularity, spreading, and signs such as blebbing and vacuoles, which are early warnings of stress or contamination. A long working-distance condenser lets even large flasks and roller bottles be viewed, and a low-power, wide-field objective helps scan whole colonies.