23 



ment, and the presence or absence of a membrane should be 

 noted. The reaction of the liquid, its consistence and odor 

 should be determined. In the agar cultures the extent of 

 the growth (feeble, moderate or vigorous,) its color, form 

 and surface appearance (dull or glistening) should be ob- 

 served. 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. 



§ 24. 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 re- 

 cording the reaction produced, neutral, acid or alkaline with 

 the degree, cover the paper with a disinfectant (a solution 

 of corrosive sublimate i to 1000). After it has acted for 

 about 10 minutes empty it with the paper into the waste jar 

 and wash the watch glass. 



To determine the viscidity. (i) Bouillon cultures. 

 Insert the platinum loop into the liquid and carefully with- 

 draw it. The approximate degree of viscidity can be de- 

 termined 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. 



§ 25. Making hanging-drop preparations, (i) From 

 bouillon culture. Place a clean cover-glass on the tray. 



