THE EXAMINATION OF MICRO-ORGANISMS 619 



differ in cultures. They reduce neutral red, do not curdle milk, pro- 

 duce acid and gas from glucose, do not attack lactose. 



Litmus milk is first acid then alkaline. 



The agglutination test is often necessary to differentiate them. 



(4) Bacillus typhosus. 



Short (2 to 4 ^), thick, rounded ends, no spores but granules and 

 vacuoles are sometimes seen. Involution forms 10 ' to 30 yu on repeated 

 sub-culture are characteristic. Aerobic and facultative anaerobic. 

 Gram-negative. Not killed by drying. Direct sunlight kills in five 

 ho'urs. On agar a thick greyish-creamy growth, on gelatin a thin 

 white growth without liquefaction, turbidity in broth with some deposit, 

 milk made slightly acid, no curdling, ferments glucose with acid but 

 no gas, lactose not affected, neutral red not affected, forms little or no 

 indol. Infects humans through water, shell-fish, dust and air, flies, 

 vegetables, soil, milk (dirty), filters, contact with carriers. 



(5) The Dysentery Bacillus. 



Fifteen tvpes are said to exist. The Flexner and the Shiga-Kruse 

 varieties are the best known. 



All resemble Bacillus coli and typhoid bacilli in morphology and 

 staining reactions. Generall}' said to be non-motile. Grow well in 

 milk without clotting, with acid then alkaline reaction. In a few days 

 ferments glucose with acid but no gas. Agglutination identifies the 

 variety. 



The Flexner type ferments mannitol with acid but no gas. 



The Shiga-Kruse bacillus has no action on this polyhydric alcohol. 



Other important micro-organisms are : — 



The Bacillus diphtheriae. 



The Klebs-Lofffer bacillus is a slender (3 to 5 /^ ) non-motile, non- 

 sporing rod with rounded ends. A parallel arrangement is common 

 and club-shaped forms are frequent. Not killed by drying. 



Aerobic and facultative anaerobic. Shows segmentation on staining 

 with Loffler's blue. Gram-positive. Shows growth on gelatin with- 

 out liquefaction, rapid growth on agar and blood serum at blood heat, 

 does not coagulate milk, forms acid therein but no gas. 



The Bacillus pestis. 



A short, thick rod, usually linked in pairs, like a cocco-bacillus. 

 Gram-negative, non-motile, no spores, bipolar staining. Grows best 

 from 25° to 20° C. Easily killed by disinfectants, cultures lose their 

 virulence quickly. In broth with a little butter flocculent tapering 

 masses of growth are seen depending upon the oil droplets floating on 

 the surface — Haffkine's stalactite growth. 



On gelatin a thick whitish punctate growth without liquefaction. 



It does not coagulate milk. 



