MORPHOLOGY 359 



motile, though it exhibits oscillatory movements which have been compared 

 to those of a compass needle. 



Staining reactions. The dysentery bacillus stains with the ordinary basic 

 aniline dyes, and with weak dyes tends to stain more deeply at the ends than 

 in the centre. It is gram-negative. 



Films should be stained with carbol-thionin or carbol-methylene-blue : 

 sections with thionin or by Nicolle's tannin method (p. 217). 



2. Cultural characteristics. 



Conditions of growth. The dysentery bacillus grows on all the ordinary 

 alkaline media, and equally well under aerobic or anaerobic conditions. The 

 optimum temperature is 37 C., though growth takes place within wide 

 limits (10-40 C.). 



Characteristics of growth. Broth. Growth is visible after incubating for 

 6 hours, and after 24 hours the medium is uniformly cloudy and has a watered- 

 silk appearance. On further incubation a small glutinous deposit forms 

 which continues to increase until towards the end of the second day, when the 

 upper part of the broth is clear : no pellicle is formed on the surface. The 

 cultures have a peculiar spermatic odour. 



Gelatin. The 'growth is like that of the typhoid , 

 bacillus. Isolated colonies are small, delicate andf 

 translucent with edges like the edges of a vin< 

 leaf. In stroke culture the growth consists of al 

 thin narrow opalescent band. The medium is not 

 liquefied. 



Agar. On agar the growth resembles that of 



+Tio HrrVhr.irl Knr>illn FlG - 215. Bacillus dysenterice. 



tne typnoid DaClllUS. Potato culture, 6 days. 



Potato. The growth on potato consists of a 



moist, shiny glaze which is at first so scanty as to be hardly visible. Later 

 it acquires a greyish or yellowish tint. 



Milk. Milk is not coagulated. 



Bacilli of the Flexner type. 



Cultures of bacilli of the Flexner type have the same characteristics as 

 but are more luxuriant than those of the Shiga bacillus. In broth, after 

 incubating for about 3 days a ring of growth adherent to the sides of the tube 

 is formed on the surface of the medium ; this falls to the bottom a few days 

 later. 



SECTION III. BIOLOGICAL PROPERTIES. 

 1. Biochemical reactions. 



Action on carbohydrates. The Shiga bacillus does not ferment carbo- 

 hydrates. The blue colour of litmus milk is unchanged, but litmus whey is 

 slightly reddened at first becoming blue again about the second or third day. 

 No gas is formed in litmus-lactose-broth. Neutral-red in glucose media is 

 not reduced. 



Bacilli of the Flexner type. These bacilli ferment mannite and maltose 

 but no other sugar [but see below] : litmus media containing mannite and 

 maltose are turned red, but no gas is formed. In lactose media they behave 

 like the Shiga bacillus. 



[All strains of the Flexner or mannite-fermenting type apparently produce 

 acid in mannite, glucose, galactose, arabinose, and raffinose : many ferment 

 (acid, no gas) maltose and dextrin though not necessarily both, while a few 



