ABSTRACT
The word 'soil' too often evokes that mineral substrate in which plants anchor their roots. It is difficult to imagine that soil constitutes a medium for life, similar to the oceans, and most people are surprised by the fact that earthworms can pass their entire life in such a habitat. Indeed, soil is currently considered a transient place: for example, the larvae of numerous insects sojourn there more or less a long time before escaping to reach free air. Many reveal their subterranean presence by the damage they cause in devouring the parenchyma of plant roots. Thanks to studies by Pasteur on sheep anthrax (caused by Bacteridium anthmcis) and the epidemiology of infectious diseases, it is also known that soil can serve as a reservoir to a large number of pathogenic agents awaiting a new host. But only in a relatively recent epoch has soil begun to be considered a permanent habitat for a multitude of living beings whose number is increasingly recognised each year.
