Anaerobic species usually require little oxygen, but aerobic species need a free supply.
It is found that if the inoculation be made deep down in a solid medium, growth of an anaerobic organism will take place, especially if the medium contains some reducing agent such as glucose.
There exist in the mud of marshes, rivers and cloacae, &c., however, other anaerobic bacteria which decompose cellulose, probably hydrolysing it first and then splitting the products into carbon dioxide and marsh gas.
As the former are only active in the air while the latter are anaerobic, the activity of either agent is conditioned by variation in the water level of the bog.
It is very probable that numerous symbiotic fermentations in the soil are due to this co-operation of oxygen-protecting species with anaerobic ones, e.g.