KINDS OF BACTERIA IN THE SOIL 125 



Potato. -Thick, white or yellowish growth, dull, becoming 

 mealy in older cultures. 



Bouillon. The liquid soon becomes turbid, and a skin forms 

 on the surface or becomes attached to the sides of the tube. 



Milk. Milk is rendered strongly alkaline, and is coagulated, 

 the curd eventually dissolving : a pellicle forms on the surface. 



Sugar. Solutions of dextrose and saccharose are made 

 acid. 



Nitrate bouillon. The nitrates are rapidly reduced to nitrites 

 and a pellicle forms. 



Bs. mycoides, Fliigge, sometimes spoken of as the root 

 bacillus, is a very common inhabitant of most soils. 



It is a stout rod-shaped bacillus, 6 to 12 & long and about 

 1.2 p broad, with almost square ends, only slightly motile as a 

 rule. It forms chains, is aerobic, and stains by Gram's method. 



The spores are oval, 1.5 to 2 & long, .8 to .9 broad. 



Gelatine. The colonies appear to be formed of fine extra- 

 ordinarily tangled threads, sometimes in the form of a circular 

 patch, but soon ramifying outwards in all directions, and very 

 much like a growth of mould. The medium is, however, soon 

 liquefied. 



The stab is whitish and characteristic, the growth extending 

 from the liquefied track in the form of delicate hairs arranged 

 parallel to each other. On the surface a felted membrane is 

 formed. 



Agar. The surface colonies in agar are at first round and 

 greyish, tangled at the edges. The stab has hair-like extensions, 

 like those in gelatine. 



Potato. The growth on potato is abundant and very closely 

 resembles that of J3s. subtilis. 



Bouillon soon becomes turbid, with a thick pellicle on the 

 surface ; later a sediment is formed and the liquid clears. 



Milk is made alkaline and the curd peptonized. 



Bs. megatherium, De Bary. This organism was originally 

 isolated from infusions of cabbage leaves and is commonly 



