{1AKING PLATE AND ESMARCH ROLL CULTURES 31 
atin is liquefied at a temperature of 45°C; (2) the plates 
en made are to be kept in the locker the same as the gelatin 
b cultures; (3) in hot weather it is sometimes necessary 
put a piece of ice in the reservoir under the glass plate on 
> leveling tripod to congeal the gelatin. 
The directions given above for making the dilutions are 
plicable only when the original culture is moderately clouded. 
there are comparatively few bacteria in the liquid, a larger 
antity of the culture will be necessary. If there are many 
ore, as in turbid bouillon or in slant-agar-culture cultures, 
will be necessary to take a much smaller quantity for the 
st dilution. It is often desirable to make the first dilution 
a tube of sterile water or bouillon instead of gelatin or agar, 
d to make 2 rather than 3 plates. It is sometimes desirable 
make 4 or more cultures. 
45. Making Esmarch roll cultures. For this purpose gela- 
. is ordinarily used. Agar does not adhere readily to the 
les of the tubes, but is sometimes used. Take the desired 
mber of large tubes of gelatin, liquefy, inoculate, label, and 
mber the dilutions as in making gelatin plate cultures. 
ace a block of ice about 6 inches long in an agate-iron or 
iss tray. Melt a slight, nearly horizontal groove in the ice 
th a test tube containing hot media or water. The inocu- 
ed tubes are tipped and rolled so that the liquid gelatin 
yistens the inside of the tube to within about a centimeter 
the plug. Then roll the tube rapidly in the groove on the 
: until the medium becomes solid. The gelatin should not 
me in contact with the plug. In rolling the tube the plugged 
d should always project beyond the ice. (See illustration in 
<t-books.) 
