158 MICROBES, FERMENTS, AND MOULDS. 
Schizophyta may therefore have two very different 
modes of existence, comparable to the heterzecia (change 
of habitat) and dimorphism of the fungi Ascomycetes 
and Basidiomycetes. Schizomycetes however, although, 
like fungi, they obtain their nourishment from organic 
substances which have been already elaborated, are 
not true parasites in the first stage of their existence, 
during which stage they live freely in the water, or on 
the damp soil. They become true parasites when they 
penetrate into the blood and tissues of man, in which 
they necessarily live at the expense of their host. 
Hence it may be seen why half-dried marshes, 
meadows from which a river has retreated in order 
to return to its bed, great excavations of the soil 
necessary in railway-cuttings, etc., become the source 
of a large number of epidemic or contagious diseases. 
In all these places the subsiding waters have left 
Schizophyta, or microbes in a dried state, and these 
are soon transformed into dormant spores, which are 
diffused through the air and enter the mouth and 
lungs of men living near the rivers and marshes, or 
who are working on the railway-cutting. The soil 
which has remained undisturbed for a long while is 
full of dormant spores, drawn into it by the rain to 
a greater or less depth; these may preserve their 
vitality for many years, waiting for the favourable 
medium which leads to their fresh development. 
An acquaintance with air-germs, with the microbes 
of earth and water, has therefore become indispensable 
