SYSTEMATIC AND DESCRIPTIVE. 147 



and remains for a time attached to the empty spore- 

 membranes. These spores are widely distributed, 

 and occur in the air, soil, dust, etc. On the 

 excrement of herbivorous animals the bacilli form 

 a white efflorescence, and on infusion of horse- 

 dung a thick crumpled skin. They flourish equally 

 in liquids and upon damp, solid nourishing media. 

 On potatoes they grow as a yellowish-white skin ; on 

 ordinary nutrient liquids they develop a thin, arid 

 subsequently a thick, dense, crumpled pellicle, with 

 copious spore-formation. They are aerobic ; depri- 

 vation of carbonic acid causes the growth of the ba- 

 cilli to cease, and the rods degenerate. They may 

 be cultivated in various other nourishing media, such 

 as blood-serum, nutrient gelatine, and nutrient agar- 

 agar (Plate XIV., Fig. 2). 



The simplest way to obtain a culture of the 

 bacillus is to make a decoction of hay. The hay 

 is chopped into small pieces, and boiled with 

 distilled water in a flask for a quarter of an hour ; 

 it is then filtered into a beaker, which must be 

 covered with a glass plate, and set aside in a 

 warm place. In two or three days the liquid 

 swarms with the bacilli, the spores of which 

 exist in great numbers in ordinary hay. A more 

 sure method for obtaining a pure cultivation is 

 as follows : 



(a) Add only a small quantity of water to some 

 finely chopped hay, and set aside for four hours 

 at 36 C. 



