76 MICRO-ORGANISMS AND DISEASE. [CHAP. 



The bacilli are capable of forming leptothrix filaments. The 

 bacilli when single are possessed of one flagellum, or some- 

 times of two, one at each end. After division the individual 

 bacilli remain connected, each possessing a flagellum at the 

 free end. Each of them divides again into four, so that a 

 chain of four is formed. But they may separate again or may 

 go on dividing, remaining united, and thus forming a longer 

 or shorter filament. Not all bacilli possess the flagellum, many 

 of them being for a time in a resting state. 



The bacilli form a dense resistent pellicle on the surface of 

 the nourishing medium, and in this copious spore-formation 



FIG. 40. FROM A CULTURK OF BACILLUS SUBTILIS (HAY-BACILLUS), WITH 

 COPIOUS FORMATION OF SPOUES. 



1. Mass of spores embedded in hyaline matrix. 



2. Bacilli. 



8. Single bacilli containing each a spore: the sheath of the bacilli is well seen. 

 Magnifying power about 700. 



takes place. If shaken when growing in a fluid, the 

 falls to the bottom, and soon a new pellicle is formed. 



Spore-formation is independent of any deficiency of nourish- 

 ing material. The spores are oval, bright, of about O'OOl to 

 0'002 mm. in length, and about 0*0006 to O'OOl mm. in thick- 

 ness. They do not stain in dyes, and hence form a great 

 contrast to the bacilli. 



This bacillus is very common and widely distributed ; it 

 occurs in almost every organic substance rich in nitrogenous 

 compounds which is left exposed to the air to decompose. The 

 best material is hay-infusion. An infusion, cold or hot, of hay 

 is made in a beaker or flask ; the fluid is filtered, covered with 

 a glass plate, and left to stand in a warm place. After a day 

 or two it swarms with bacillus subtilis, which is also called 

 hay-bacillus, since ordinary hay contains multitudes of its 



