• K. M. DoiDGK 69 



The size of the colonies is very much affected by crowding. (Plate 

 XIII, b, c, d.) 



Nutrient agar streak. A well developed agar streak appears in 24 

 hours at 25° C. : it is smooth, shining, about 3 mm. wide and grumose 

 in the centre. In three days this has become 3 — 5 ram. broad, 

 primuhne yellow, the central part being pulvinate. and the margin 

 entire or shghtly undulate. 



After 12 days the surface of the agar has become very decidedly 

 whitened except for the parts covered by the bacterial growth ; long 

 feathery crystals point downwards into the medium from the under 

 surface of the streak. The condensation water is very heavily clouded. 

 A second kind of crystal is formed on the surface of the agar under 

 the condensation water, very similar to those illustrated by Smith as 

 occurring in cultures of the olive tubercle organism (7). 



The texture of the streaks in three weeks old culture varies very 

 much with the amount of water present in the medium and in the 

 atmosphere. Some remain creamy, but contain small tough moruloid 

 masses; others become very tough at an early stage, large strips may 

 be pulled away on the platinum needle and when this is done the growth 

 stretches somewhat and has the appearance of a number of spherical 

 colonies in a tough homogeneous matrix. Most commonly the growth 

 is raised and almost homogeneous to the naked eye. It is then very 

 mucilaginous, and in colour and texture is not unhke plastic sulphur. 



If the surface of the sloped agar be bathed in lemon or orange oil 

 a very luxuriant growth is obtained which does not become tough or 

 mucilaginous. 



Nutrient agar stab, the best growth is at the surface. 



Glucose formate agar. Streaks were made on this medium as a 

 control for those kept under anaerobic conditions; the growth is very 

 similar to that on ordinary nutrient agar, but shghtly more luxuriant. 



Sulphindigotate agar. This medium was used for a similar purpose ; 

 a very luxuriant growth was obtained, on the upper drier portion of 

 the slope a number of small discrete colonies were produced which at 

 first absorbed the colouring matter from the medium and became 

 blue. The lower part of the slope was almost covered by a wet shining, 

 yellowish growth which was grumose in the centre. The colour gradu- 

 ally disappeared from the medium. 



Lemon and Orange glucose agar. Colonies on these media are 

 similar to those on nutrient agar but considerably smaller, only 2-3 mm. 

 in diameter after three days; they are very markedly umbonate in 

 Ann. Biol, in o 



