MICROSCOPIC EXAMINATION 121 



needle and carefully rinse it in the drop of liquid on the 

 cover-glass. From this point the examination is the same as 

 with the liquid culture. Upon examination, if the bacteria 

 are so numerous that the individual organisms cannot be 

 clearly distinguished from each other, the preparation should 

 be rejected and another one made, using a smaller quantity 

 of the growth. After examination, the cover glasses should 

 be placed at once in a strong disinfectant. 



In the examination of bacteria in these preparations one 

 can determine the shape of the individual bacteria and also 

 whether or not they are single or appear in pairs, clumps or 

 in short or longer chains. It is also possible to determine 

 whether or not they are motile or possessed of a distinct 

 capsule. In the examination of the hanging drop preparation 

 it is desirable to move the slide so that one studies the or- 

 ganism at the edge of the drop. Many details in the mor- 

 phology of bacteria can not be determined in these prepara- 

 tions. Thus the flagella and usually the capsule are not in 

 evidence on bacteria possessing them unless they are specially 

 stained. It should be noted that certain species of bacteria 

 take the stain less readily and more unevenly than others. 



The hanging block culture. In order to study the 

 morphology and the manner of multiplication of bacteria to 

 better advantage than in the hanging drop, Hill x devised 

 the following procedure: "Melted nutrient agar is poured 

 into a Petri dish to a depth of about one-eighth to one-quarter 

 of an inch. "When cool, a block is cut out about one-quarter 

 of an inch square. The block is placed under surface down 

 on a slide and protected from dust. A suspension of the 

 growth to be examined is then made in sterile bouillon and 

 spread over the upper surface of the block. The slide and 

 block are then put in the incubator for ten minutes to dry 

 slightly. A clean cover-slip is now placed on the agar block 

 in such a way as to avoid large air bubbles. The slide is 

 then removed. With the aid of a platinum loop, a drop or 



1 Hill. Jour, of Medical Research, Vol. VII (1902) p. 202. 



