342 LABORATORY WORK 
No. 18. Fermentation Tubes.—Prepare 200 c.c. of bouillon as described in 
No. 2, adding to it 2 grams lactose and adjust the reaction to the neutral point. 
To a second lot of bouillon add the same amount of dextrose and to a third lot the 
same amount of saccharose. After dissolving and filtering pour into fermentation 
tubes, enough to fill the closed arm and half the bulb (Fig. 63). A dozen or more 
tubes of each of these bouillons should be prepared and labeled. Sterilize by steam- 
ing on three days, or by not over 1§ minutes 
in the autoclave. If gas collects in the closed 
arm remove by tilting the tube. 
No. 19. Testing Characters of Bacteria.— 
Several isolated and purified cultures of bacteria 
have been prepared in No. 7. After having 
prepared the several culture media above de- 
scribed, use them as follows: Make a fresh 
agar slant from each purified bacterial culture 
and allow to grow about 24 hours. If possible 
use a culture of B. coli for one of the series of 
tests. Then inoculate with a small quantity 
i NN of the growth the following: 
ese =e (2) Two agar slants. (6) One gelatin stab. 
z, This is made by dipping a straight platinum 
needle into the bacteria and then thrusting it 
straight into the gelatin of a gelatin tube, in 
the middle of the tube, and forcing the needle 
to the bottom, carefully withdrawing without 
Fic. 63.—-Fermentation tube with disturbing the gelatin. (c) A fermentation 
closed arm containing gas. tube of each of the three sugars. (d) Two milk 
tubes. (e) Twolitmus milktubes. (f) Two po- 
tato tubes, inoculating the potato onitssurface only. Place one of the agar tubes, one 
of the milk tubes, litmus milk tubes, and potato tubes in the incubating oven at 
98°. Place all others at room temperature. Allow to grow several days, examining 
each day. For each species of bacterium note the following points: 
A gar Slants; Color. Is growth thick or thin, moist or dry; does it spread? 
Morphology.—With the microscope study stained specimens; note shape—forma- 
tion of chains—spores. Determine motility. 
Gelatin Siab.—Note liquefaction, needle growth, surface growth. Compare 
growth with Fig. 34. 
Bouitllon.—Note turbidity, scum, sediment. 
Milk Tubes.—Note at 98° and 70° the development of acid as shown by its action 
on litmus, curdling, separation of whey, appearance of gas bubbles, subsequent 
softening and solution of the curd, called digestion. 
Potatoes —At 98° and 70°, note color, abundance of growth, texture of growth, 
discoloration of potato. 
Fermentation Tubes.—After several days note whether gas has collected in the 
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