KINDS OF BACTERIA IN THE SOIL 129 



ing the surrounding medium a brown colour. The borders have 

 a fringe of filaments round them. 



Slight liquefaction of the medium occurs in a week or ten days. 



It grows well on gelatine medium (4 to 4.5 per cent, gelatine), 

 to which a very small amount of Lemco has been added ; also 

 in dilute bouillon. 



Agar. Whitish colonies, with wrinkled skin-like surfaces ; the 

 agar stained brown. 



Potato. Thick grey growth, with brown staining of the potato. 



Bouillon, White flaky colonies, slowly produced in it ; the 

 medium is coloured a rich deep brown tint. 



Milk. Slowly made acid ; probably peptonized also. 



Other species isolated from soil are Cladothrix rufula, Wright, 

 which colours media pinkish ; Cl. profundus, Rav., and Cl. 

 \ntestinalis, Rav., which stain the media brownish ; C. fungi- 

 ) Rav., which does not stain the medium. 



Ex. 70. Dig up a spadeful of soil from 



1. A sandy field. 



2. A field of medium loam. 



3. A field of stiff clay. 



4. A well manured garden. 



5. A peaty heath. 



Transfer untouched portions of the soil dug up to sterilized 

 wide-mouthed bottles. 



From each of these samples take about 10 grams, and drop 

 them into separate flasks containing 250 c.c. of sterile tap water ; 

 shake well. 



Then remove io c.c. of the turbid water with a sterilized 

 pipette, and add it to another flask containing 250 c.c. of sterile 

 tap water : shake well. 



Repeat the dilution once again, i.e. 10 c.c. of the latter mixture 

 into 250 c.c. of water in a third flask. 



From this third dilution take i c.c. and inoculate an agar plate 

 with it. 



