AEROBIC SPORE-BEARING NON-PATHOGENIC BACTERIA 285 



and thus bulge the rods slightly. The free spores retain their 

 protoplasm at the ends for some time, usually in equal amounts. 

 Often, however, the protoplasm is greater at one end than at the 

 other and the spore then has a characteristic appearance like 

 an enlarged mesentericus spore. The free spores are cylindrical, 

 soon shed their protoplasm and measure 0.5 to 0.75 by 1.125 to 

 1.5 microns. 



Agar slant. Abundant, thick, white mealy growth along the 

 line of inoculation sometimes with arborescent edges. In older 

 cultures the growth is much thicker, yellowish white and may 

 show pellucid areas surrounded by more highly refractive patches. 



Agar stab. Little growth along line of inoculation but luxuri- 

 ant surface growth spreading over entire surface of agar and 

 extending to the walls of the tube. 



Agar colonies. Round, raised, dense, highly refractive sur- 

 face colonies. If slight amount of water of condensation be 

 present the colonies may be amoeboid. Under low power the 

 colonies consist of dense central nuclei with spreading peripheries 

 made up of numerous curling and parallel chains. The colonies 

 are soft and easily hf ted from the agar. Deep colonies punctiform, 

 stellate or rhizoid. Under the low power they are fuzzy, irregu- 

 lar and may resemble a chestnut burr. 



Litmus glucose agar slant. Thick, yellowish-white growth 

 along the line of inoculation and spreading out over entire surface. 

 The medium is acidified and the growth is sometimes distinctly 

 yellow. Typical cultures rapidly decolorize the litmus and then 

 become alkaline and the agar turns deep blue. Occasionally 

 the cultures are less active alkali-producers and the medium 

 remains permanently acid. Such cultures, however, can usually 

 be stimulated to alkali production by plating and they then give 

 characteristic growths. 



Glucose agar colonies. Surface colonies round or bizarre, 

 heaped up, with irregular margins, smaller than plain agar 

 colonies. Under low power granular, with dense central nuclei 

 and irregular margins, showing fine parallel strands. Deep colo- 

 nies small irregular or round. Under low power they consist of 

 dense central nuclei with fine, irregular or parallel strands in the 

 periphery. 



