128 



BACTERIOLOGY OF THE SOIL 



(t 



Milk. Becomes slightly acid after two or three weeks without 

 coagulation. 



Cladothrix dichotoma, Cohn. This organism belongs to 

 Chlamydobacteriaceae, a family of organisms included among the 

 bacteria, but showing much affinity with the blue-green Algae. It 

 is met with in the form of long cylindrical threads from i to 



3 ^ in diameter and i to 2 mm. 

 long, attached at one end to 

 bits of sand, earth, or vegetable 

 debris, in water and damp soil. 



Each thread consists of a 

 gelatinous sheath, which en- 

 closes rod-shaped cells, 3 to 8 //, 

 long and i to 2.5 //. broad, 

 arranged end to end throughout 

 its whole length (Fig. 28). 



The free ends of the thread 

 appear to be branched dicho- 

 tomously; this arises not through 

 a true division of the growing 

 point, but is brought about by 

 some of the cells in the sheath 

 dividing and growing out later- 

 ally into new filaments. 



Some of the cells leave the 

 sheath, becoming flagellated or- 

 ganisms, which swim about for a time ; later these settle down 

 and begin to divide and form new threads. 



C. dichotoma is not infrequent in water pipes and drains, 

 and one or more closely related kinds are sometimes found in 

 the soil : the " Bismarck brown " Cladothrix of Houston, is 

 probably identical with this species. 



Gelatine. The colonies are white, small, from. 5 to 2 mm. in 

 diameter, slow in growth, usually with a brown centre, and stain- 



FlG. 28. Cladothrix dichotoma, Cohn. 



1. As seen under low magnification 



( X 100). 



2. Highly magnified (Xyso), show- 



ing sheath enclosing cells of 

 organism. 

 a Cells free from sheath. 



