CULTURAL CHARACTERISTICS 165 



He found the relative number of these organisms occurring in 

 soils to be as follows: 



1. From 5 to 10 per cent, spore-formers (the B. subtilis group). 

 Nearly all the colonies of these bacteria, however, seem to come from 

 spores instead of from active organisms. 



2. Under 10 per cent, rapidly liquefying, non-spore-forming, 

 short rods with polar flagella (principally Ps. fluorescens) . 



3. From 40 to 75 per cent, slowly liquefying or non-liquefying, 

 non-spore-forming, short rods. 



4. A few micrococci. In cultural characteristics these are almost 

 identical with the last mentioned group. 



5. From 12 to 50 per cent. Actinomycetes. 



The most abundant spore-formers found in the soil and described 

 by Conn were B. megatherium De Bary, B. mycoides Fliigge, B. 

 cereus Frankland, and B. simplex Gottheil. 



"B. megatherium De Bary, 1884. This species is to be distin- 

 guished from B. mycoides and B. cereus by the larger average size 

 of its spores, by its poor growth in liquid media, its failure to grow 

 in the closed arm of fermentation tubes of dextrose broth, and by 

 its comparatively slow liquefaction of gelatin. 



"Morphology. Very young cultures (under twelve hours) consist 

 of large rods about 1 to 1.5 M in diameter and about 3 to 6 /* 

 long. They often occur in chains with connecting threads be- 

 tween the rods, resembling strings of sausages. In older cultures 

 the rods generally become swollen and are sometimes full of highly 

 refractive globules (fat drops?). One of the most distinctive 

 characteristics is the presence in cultures a day or more old of 

 large ovoid bodies about 2 by 4 /z in size, which seem to have 

 heavy walls and stain much more lightly than the young rods. 

 Only the young rods are motile, and they are not vigorously so. 

 The flagella are difficult to stain, and the best preparations made 

 show comparatively few flagella on each rod. Spores are formed in 

 the center of the rods and immediately become free from all trace of 

 the sporangium wall. They are oval to ovoid (or occasionally 

 reniform) and vary considerably in size, from 1.3 to 2 //, in diameter 

 and from 1.5 to 3 ju in length, both extremes often occurring in the 

 same preparation. 



"Cultural Characteristics. Growth in broth flocculent or none, 

 with no surface growth. Gelatin colonies under 10 mm. in diameter, 

 center white, opaque, flocculent or granular, surrounded by a clear 

 liquefied zone. Growth on agar streak cultures smooth, soft, glisten- 

 ing, cream-color, typically with minute drop-like areas of lighter 

 color. 



"Physiology. The typical group number is B. 111. 44420 ?4. As 

 indicated by this group number, there is ordinarily no growth in 

 sugar and glycerin broths. This does not mean, however, that no 



