444 BACILLUS WELCHII 



readily stained with the basic dyes, and is Gram -positive, 

 though in older cultures Gram -negative forms occur. In 

 the tissue fluids it usually has a distinct and fairly broad 

 capsule, hence the original name; sometimes, however, no 

 capsule is seen ; the presence or absence of the capsule depends 

 on conditions already referred to (p. 228). In ordinary media, 

 again, no capsule is seen, but in serum media it can be demon- 

 strated by special methods (c/. pneumococcus). The organism 

 is non-motile, and no flagella have been demonstrated. 



In the spreading area of the disease no spores are found, 

 though they have been described in the later stages when the 



bacillus is associated 



-- / " "-^ with other organisms. 



"~iL^ *"~" x At first it was believed 



U ^^(\ I not to form spores, but, 



^\ , %•. — \ as was first shown by 



>> ^. ^ — — j 



— \J j" \ \ / Dunham, spores are pro- 



\ s ( v \ If duced in serum media; 



\f ^^y / ^ey are ova ^ anc ^ ^ au *iy 



f~/. // \ C W/f ' lar 8 e > usually subter- 



V I » (A . X/ \ . minal, occasionally 



( - L ^ I ^ J J central. In ordinary 



^^ /**£ / i fc»0«> \ \ media, however, and in 



\ "N" jjwV' H X — tae P resence °^ a trace 



\^7"' v ^ , * s * ?f Ss » of sugar, no spores are 



*""*v/ ^«. i V > formed. 



1 Cultivation. — The 



Pig. 127.— Film from a pure culture of bacillus welchii can 



b. welchii. , ... 



Gram's stain. xlOOO. be readily grown on 



various media, but only 

 under strict anaerobic conditions. It flourishes best at the 

 temperature of the body, but grows also at room temperature. 

 On serum agar the superficial colonies are circular in form, 

 moist in appearance, with smooth margins, there being no 

 radiate outgrowth or downgrowth; the deep colonies are 

 usually oval or lenticular in form, with sharp outline. It 

 produces no liquefaction either in gelatine or in solidified 

 serum. In milk the characters of the growth are of import- 

 ance. It grows rapidly and leads to production of coagula- 

 tion of the medium, the clot becomes broken up by gas 

 bubbles — the so-called " stormy reaction " — and ultimately 

 comes to form irregular tough masses bathed in comparatively 

 clear whey. There is no digestion of the casein even after a 

 long time. The culture has an odour of butyric acid. These 



