262 MICRO-ORGANISMS AND DISEASE [chap. 



be carried on ; although in other cases after about a dozen 

 generations in broth no living sub-cultures could be made 

 in broth. 



2. Culture 091 Agar. — The cultivations and sub-cultiva- 

 tions were (a) on beef broth (not beef infusion), Agar (i p.c), 

 peptone (i p.c), and salt (i p.c.) ; and {b) on glycerine 

 Agar, that is the ordinary Agar plus glycerine (6 p.c). 

 The growth on our ordinary Agar is rather more easily 

 observed than on glycerine Agar, being a little more 

 copious (the colonies being somewhat larger) and a little 

 less translucent, and therefore more readily noticeable. 



The colonies on the surface of both these media can be 

 discerned under a glass after twenty-four hours' incubation 

 at 37" C. They then have the appearance of extremely 

 minute translucent flat droplets, and these during the next 

 day or two increase somewhat in size, but even at their 

 largest are but small — not exceeding three millimetres in 

 breadth, and only just visible to the eye as translucent 

 circular flat droplets — on further incubation becoming 

 flatter (Fig. 99). Under a lens their margin is seen to 

 be slightly crenated and their centre darker than the rest. 

 The crenated margins show no tendency to coalesce, even 

 when the colonies are thickly planted. 



In Agar stab-culture the stab is indicated after two or 

 more days as a grey line, this being made up of granules 

 densely and closely placed ; viewed under a glass, minute 

 club-shaped and pear-shaped projections are seen to 

 extend from the dark line of inoculation. In stab- 

 cultures, as in surface growths, the several colonies are a, 

 little more copious and less translucent when our ordinary 

 Agar is used for the cultivations than when glycerine has 

 been added. 



The condensation water in the Agar tubes (of ordinary 



