284 BACTERIOLOGY. 



in the throat that at the end of twenty-four hours they 

 are often the only colonies that attract attention, and if 

 others of similiar size are present, they are generally of 

 quite a different aspect. Its colonies are large, round, 

 elevated, grayish-white, or yellowish with a centre more 

 opaque than the slightly irregular periphery. The sur- 

 face of the colony is at first moist, but after a day or 

 two becomes rather dry in appearance. 



A blood-serum tube studded over with coalescent or 

 scattered colonies of this organism is so characteristic 

 that one familiar with the appearance can anticipate 

 with tolerable certainty the results of microscopic ex- 

 amination. 



Glycerin-agae-agae. — Upon nutrient glycerin- 

 agar-agar the colonies likewise present an appearance 

 that may readily be recognized. They are in every way 

 more delicate in their structure than when on the serum 

 mixture. They appear at first, when on the surface, as 

 very flat, almost transparent, dry, non-glistening, round 

 points which are not elevated above the surface upon 

 which they are growing. When slightly magnified 

 they are seen to be granular, and present an irregular 

 central marking which is more dense and darker by 

 transmitted light than the thin, delicate zone which 

 surrounds it. As the colony increases in size the thin 

 granular peripheral zone becomes broader, is usually 

 marked by ridges or cracks, and its periphery is notched 

 or scalloped. (Fig 55, e.) These colonies are always 

 quite dry in appearance. When deep down in the agar- 

 agar they are coarsely granular. (Fig. 55, a.) They 

 rarely exceed 3 mm. in diameter. 



Gelatin. — On gelatin the colonies develop much 

 more slowly than on the other media which can be 



