STAINING TECHNIQUE v7 
Hanging Block. This preparation allows the bacteria to develop 
but prevents their movement and thus holds them in one place for 
observation. In this way the relation of cell to cell may be studied. 
They may be prepared in the following manner. A sterile agar plate 
is poured and allowed to harden. From this by means of a sterile 
scalpel or spatula is cut a block of the agar which is picked up on the 
spatula. On its surface is rubbed a small amount of the culture which 
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Fre. 30.—Types of Concave Slides and Moist Chambers for Making Hanging Drop 
and Hanging Block Mounts. 
is under study. The agar block is then put up on a sterile cover glass 
in such a way that the cells of the organism will be between agar block 
and the cover glass, cover slip. About the edge of the cover slip 
should be placed a small amount of vaseline to hold the slip in place 
and also to prevent evaporation if the mount 1s to be incubated. These 
preparations may be kept for some time if desired. Hill (1902) has 
discussed the application of this preparation to the observation of 
developing bacteria. 
