

BACTERIA IN THE DAIRY. AQ 
for a short distance into the surrounding medium. In some 
instances there will be a dark centre surrounded by a lighter 
rim. ‘Their size is always less than one millimeter. ‘The more 
common appearance under the microscope is a dark-colored, 
spiny, slightly yellowish colony, homogenous in density. ‘hey 
never appear to grow on the surface, but, in some cases, very 
near the surface, with a thin layer of gelatine above it raised 
by the growth of the colony. 
II.—ORDINARY GELATINE. 
There is produced in this medium a small circular colony 
which is finely granular; pearly white by reflected light, and 
slightly yellowish by transmitted light. The growth is very 
slow. 
MORPHOLOGY. 
In bouillon there appear short plump rods, many of them in 
figure 8’s, some in chains of three to six in number. ‘To make 
these, a rod, after lengthening, partially breaks up into five or 
six. The common method of multiplication is, for a rod to 
lengthen and divide in the middle, the connection between the 
two remaining for some time. Average size is 1.24 long by 
.7u wide.* | 
| MOTILITY. 
They are never motile. 
| TEMPERATURE. 
The growth is very rapid in milk at temperatures from 28° 
to 37%° C. On agar-agar they do not grow so rapidly ata 
high temperature, and even, in some instances, do not grow 
on the surface of agar-agar at 37%° C. 
RELATION TO AIR. 
They grow more vigorously out of contact with the air, 
under mica plates producing more acid than in free gelatine. 
GELATINE STAB CULTURES. 
Growth entirely below surface along the needle track, which 
is abundant, beady, rough, and densely white. 
AGAR-AGAR TUBES. 
It grows on the surface of agar-agar very scantily, not more 
than one or two mm. wide, in avery thin layer. If held to the 


* vu, equals of an inch. 
25,000 
