This activity, and the maintenance of those houses, required a large labor force.

They had to be, if only because the daily maintenance of household technology in such a hostile environment required it.

Some maintenance may require that the web server be unavailable for the entire hour.

Very little maintenance is required and no (or greatly reduced) amounts of chemicals.

Maintenance of liquid surface water also requires a sufficiently thick atmosphere.

Yet the parks' intensive maintenance requires a commitment of resources that may be hard to match elsewhere.

The maintenance of a gold standard required almost monthly adjustments of interest rates.

The maintenance of the dam requires the constant attention of the owners.

Maintenance of blue iguanas in the wild requires active management into the indefinite future.

Thus, maintenance of health requires the body to recognize all pathogens (antigens they present or produce) likely to exist.