1 8 LABORATORY BACTERIOLOGY 



masses held in suspension, the quantity and nature of sedi- 

 ment, and the presence or absence of a membrane. The 

 reaction of the liquid should be taken and its consistence 

 noted. The odor should be determined. In agar cultures 

 the extent of the growth (feeble, moderate, or vigorous), its 

 color, form, and surface appearance (dull or glistening), 

 should be observed. The character of the growth in the 

 condensation water should also be noted. In stab cultures 

 the appearance of the growth both on the surface and along 

 the needle track should be described. In gelatin, the absence 

 or the presence and extent of liquefaction should be noted 

 in addition to the features already referred to for the stab agar 

 cultures. 



26. Testing the Reaction of Liquid Cultures. — Place a small 

 piece of each of the red and blue litmus paper in a solid watch 

 glass. With the platinum loop carefully place a drop of the 

 culture on each piece of the paper. After recording the re- 

 action produced, neutral, acid, or alkaline with the degree, 

 cover the paper with a disinfectant (a solution of corrosive 

 sublimate i to looo). After it has acted for about lo min- 

 utes, empty it with the paper into the waste jar and wash the 

 watch glass. 



27. To determine the Viscidity. — (i) Bouillon cultures. 

 Insert the platinum loop into the liquid and carefully withdraw 

 it. The approximate degree of viscidity can be determined 

 by the extent of the adhesion of the liquid to the loop, and 

 the length of the thread-like filament drawn out. By gently 

 shaking the tube a viscid sediment will rise up, appearing as a 

 somewhat twisted, tenacious cone with its apex reaching to or 

 near the surface. A friable sediment will break up and become 

 disseminated through the liquid upon agitation. (2) Agar 

 and gelatin cultures. Touch the surface growth with the end 

 of the platinum needle, and if it is viscid, a thread-like string 

 will be drawn out. Note whether the growth is pasty or 

 friable. 



