NOT DESCRIBED IN PREVIOUS SECTIONS. 531 
temperature—more rapidly in the incubating oven. Grows in a de- 
cidedly acid medium. 
In gelatin plates colonies are developed in from twenty-four to 
forty-eight hours, which vary considerably in their appearance ac- 
cording to their age, and in different cultures in the same medium. 
The deep colonies are usually spherical and at first are transparent, 
homogeneous, and of a pale-straw or amber color by transmitted 
light ; later they frequently have a dark-brown, opaque central por- 
tion surrounded by a more transparent peripheral zone ; or they may 
be coarsely granular and opaque; sometimes they have a long-oval 
or ‘‘whetstone” form. The superficial colonies differ still more in 
appearance ; very young colonies by transmitted light often resemble 
little drops of water or fragments of broken glass ; when they have 
sufficient space for their development they quickly increase in size, 
and may attain a diameter of three to four centimetres ; the central 
portion is thickest, and is often marked by aspherical nucleus of a 
dark-brown color when the colony has started below the surface of 
the gelatin; the margins are thin and transparent, the thickness 
gradually increasing towards the centre, as doesalso the color, which 
by transmitted light varies from light straw color or amber to adark 
brown. The outlines of superficial colonies are more or less irregular, 
and the surface may be marked by ridges, fissures, or concentric 
rings, or may be granular. The writer has observed colonies re- 
sembling a rosette, or a daisy with expanded petals. Escherich 
speaks of colonies which present star-shaped figures surrounded by 
concentric rings. 
In gelatin stab cultures the growth upon the surface is rather 
dry, and may be quite thin, extending over the entire surface of the 
gelatin, or it may be thicker with irregular, leaf-like outlines and 
with superficial incrustations or concentric annular markings. An 
abundant development occurs all along the line of puncture, which 
in the deeper portion of the gelatin is made up of more or less closely 
crowded colonies ; these are white by reflected light, and of an am- 
ber or light-brown color by transmitted light ; later they may become 
granular and opaque. Frequently a diffused cloudy appearance is 
observed near the surface of the gelatin, and under certain circum- 
stances branching, moss-like tufts develop at intervals along the line 
of growth. One or more gas bubbles may often be seen in recent 
stick cultures in gelatin. 
Upon nutrient agar and blood serum, in the incubating oven, an 
abundant, soft, white layer is quickly developed. Upon potato an 
abundant, soft, shining layer of a brownish-yellow color is developed. 
The growth upon potato differs considerably, according to the age of 
the potato. According to Escherich, upon old potatoes there may 
