THE DIVISION AND POST-FISSION MOVEMENTS 
OF BACILLI WHEN GROWN ON SOLID MEDIA. 
By G. S. GRAHAM-SMITH, M.D. 
(University Lecturer in Hygiene, Cambridge). 
(Plates III—VIII and 14 Text-figures.) 
The behaviour of living bacteria during artificial cultivation in 
fluid and semi-solid media has often been observed and described, but 
very few investigators appear to have studied the changes which take 
place when bacteria are grown either on the surface or in the depth of 
solid media. The investigations which are described in this paper were 
undertaken with the purpose of ascertaining how various bacilli behaved 
during the early stages of growth on the surface and in the depth of 
agar, and how far the various types of division and post-fission move¬ 
ment influenced the characters of the colonies subsequently formed. 
Hill (1901) devised a method for watching the growth of bacteria 
on agar and carefully described the mode of growth of B. diphtheriae 
and of B. typhosus. His “ technique consists briefly in substituting for 
the ordinary ‘ hanging drop ’ of liquid or jelly a cube of solidified agar, on 
the surface of which the bacteria are distributed. The inoculated surface 
of this cube is applied to the under surface of a cover-slip, and for 
convenience is known then as the ‘hanging block.’ Oxygen probably 
reaches the bacteria by diffusion through the block or the seal. Certainly 
aerobic bacteria like B. diphtheriae, B. typhosus, etc., grow readily in 
such preparations.” 
Hill (1902, p. 204) gives the following directions for preparing 
hanging block preparations. “ Pour melted agar into a Petri dish to 
the depth of about one-eight to one-quarter inch. Cool this agar and 
cut from it a block about one-quarter inch to one-third inch square and of 
Parasitology iii 
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