120 MICROBES, FERMENTS, AND MOULDS. 
abundantly supplied to them, the microbes are very 
mobile; as soon as the quantity of sulphur diminishes 
they become less mobile, and reconsume the sulphur 
they have stored up; finally, they become quite 
motionless—a phenomenon concomitant with the forma- 
tion of spores. Within each cell of the filamentous 
alga there is a minute sphere, brilliant and refracting, 
of which the development is in inverse ratio to the 
quantity of sulphur in the surrounding liquid. These 
spores become free in the form of chaplets, after the 
destruction of the cell-wall, and these chaplets are 
precisely like those of Bacillus subtilis. 
Planchud was the first to whom it occurred to 
look for a special ferment in the glairine or barégine 
which may be seen floating on the surface of sul- 
phurous waters. He showed that one gramme of car- 
bolic acid to a litre of water arrests the reduction of 
the sulphates into sulphur, and that this reduction is 
resumed as soon as the carbolic acid has evaporated. 
Six grammes to the litre completely destroy the 
Sulphuraria, as these alge are termed by Planchud. 
This observer also performed experiments which 
led him to believe that the same alge will reduce 
gypsum to native sulphur, and that the vast deposits 
of sulphur found in certain regions are due to the 
action of this microscopic plant. It is now well 
known that a chemical action of the same nature, 
the production of saltpetre, is the work of similar 
microbes. 
