120 MICEOBES, 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 suhtilis. 



Planchud was the first to whom it occurred to 

 look for a special ferment in the glairine or baregine 

 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 algse are termed by Planchud. 



This observer also performed experiments which 

 led him to believe that the same algse wiU reduce 

 gypsum to native sulphur, and th^t 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. 



