292 PRACTICAL DAIRY BACTERIOLOGY 



will appear a white mold. This grows more slowly than the 

 Oidium, and its threads do not break up into spores. Spores 

 form on the surface upon special branches. (See Fig. 63.) 



Both the Oidium and mold may be isolated for future study 

 if time permits. 



No. 25. Abnormal Fermentations. If any unusual types of 

 fermentation can be found, like slimy milk, bitter milk, tainted 

 milk, etc., they may be studied to advantage. Gelatin plates 

 should be made from such milk and the different kinds of colo- 

 nies isolated. After purifying, these should be inoculated into 

 sterile milk to see if any of them produce the trouble seen in 

 the original milk. If such is found it may sometimes be traced 

 to its source by hunting for it in various places around the 

 dairy ; e. g., in the milk cans cows' teats dairy water hay 

 dust, etc. No definite directions for this can be given, for each 

 problem will need different treatment. 



*No. 26. Potato Tubes. Carefully wash and peal a large po- 

 tato. With a special cutter (Fig. 83), or with a broken test tube 

 with sharp edges, cut out some potato plugs. Cut each obliquely 

 in two parts and soak in running water 12 hours. In the bottom 

 of some large test tubes place a little cotton and enough water 

 to cover it. Place a single potato slant in each tube (Fig. 83) 

 and sterilize by one-half hour steaming on three successive days. 



*No. 27. Fermentation Tubes. To 200 c.c. of bouillon pre- 

 pared as in (4) add 2 grams of lactose (milk sugar). To a sec- 

 ond 200 c.c. add the same amount of dextrose (grape sugar), and 

 to a third lot add saccharose (cane sugar). Dissolve by heating 

 filter through filter paper and pour into fermentation tubes 

 (Fig. 20), completely filling, the closed arm and about one- 

 half the bulb. Sterilize as usual. If gas collects in the arm, 

 remove by tilting the tube. 



*No. 28. Milk Tubes. Procure some fresh skimmed milk. Test 

 the reaction with litmus paper and if acid add sufficient NaOH 

 to bring to neutral point of litmus paper. Place in tubes, about 



