CULTURES IN SOLID MEDIA. V1 
or in its absence—a facultative anaérobic. In the third case the 
microérganism is an anaérobic, which cannot grow in the presence 
of oxygen, and consequently does not grow upon the surface of the 
culture medium or along the upper portion of the line of puncture. 
Again, we have differences as to the character of growth upon the 
surface or along the line of puncture. The surface growth may be 
a little mass piled up at the point where the needle entered the gela- 
tin; or it may form a layer over the entire surface, and this may 
be thin or thick, dry or moist, viscid or cream-like, and of various 
colors—green, blue, red, or yellow, of different shades—or more fre- 
quently of a milk-white color. 
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Fre. 41 
The growth along the line of puncture also differs greatly with 
different species. We may have a number of scattered spherical 
colonies (a, Fig. 41), and these may be translucent or opaque ; or we 
may have little tufts, like moss, projecting from the line of puncture 
(b, Fig. 41) ; or slender, filamentous branches may grow out into the 
gelatin (c, Fig. 41). 
The liquefying bacilli also present different characters of growth. 
Thus liquefaction may take place all along the line of puncture, 
forming a long and narrow funnel of liquefied gelatin (a, Fig. 42) ; 
or we may have a broad funnel, as at b ; or a cup-shaped cavity, as 
at c,; or the upper liquefied portion may be separated from that 
which is not liquefied by a horizontal plane surface, as at d. 
