BACILLUS PKODIGIOSUS 343 



somewhat in size, the largest organisms being about 1"7 m 

 long hy 1 fA, broad. They are frequently seen in pairs, 

 are non-motile. The organism grows well on all the 

 ordinary media. The production of the blood-red colour 

 is governed by the temperature and by the presence of 

 oxygen, as well as by the nature of the nutrient medium. 

 The colour decreases in cultures kept at incubation tem- 

 perature. By long-continued growth on artificial media, 

 the organism often loses' its power of pigment production, 

 which may, however, often be restored by cultivation on 

 potatoes. Cultures give off an odour of trimethylamine. 

 Cultural characters : 



Gelatine Plates. — After two days the colonies are visible 

 as circular depressions, each having a red centre. The 

 less developed colonies in the depth are seen to be devoid 

 of colour. 



Gelatine Tubes. — The growth is very rapid, the gelatine 

 liquefying in the form of a circular, funnel-like tube, the 

 whole contents of the tube soon becoming liquid. The 

 liquefied gelatine is very turbid, it containing an abundant 

 deposit of a crimson colour. 



Agar-Agar. — Grows rapidly, producing a blood-like ex- 

 pansion, the growth being restricted to the surface. 



Potatoes. — Luxuriant growth of a beautiful crimson 

 colour, which afterwards develops a metallic lustre. 



Proteus Vulgaris. — This organism is found in putrefying 

 animal substances, sewage, water, etc. It forms slightly 

 bent bacilli about 0'6 /u. broad and of variable length up to 

 3"8 fi ; also gives rise to snake-like threads, resembling 

 plaits of hair. It has a great tendency to form involution 

 forms. The organism is very motile. Cultural characters : 



Gelatine Plates. — The colonies are yellowish-brown in 

 colour, bristling edges, which afterwards throw out irregular 



