BACILLUS COLI 47 



occurring on ordinary gelatine, except that they grow more slowly, are more 

 circumscribed, and of a characteristic brown colour (Houston). 



On carbol-gelatine ('05 per cent, of phenol), the growth does not differ from 

 ordinary gelatine cultures except that it is delayed. 



Broth In less than twelve hours at 37 C. the medium becomes uniformly 

 turbid. It may be very pronounced. Frequently there is also at a later 

 stage a marked amorphous flocculent sediment consisting of bacteria. Only a 

 faint film forms on the surface, which rarely becomes a pellicle. There is a foetid 

 odour, and sometimes gas formation. In glucose, lactose, saccharose broth 

 (2 per cent), and glucose-formate broth (Pakes), and bile-salt broth (M'Conkey), 

 the growth is abundant, and gas is produced. In phenolated broth ('05 per 

 cent, of phenol), and in broth containing formalin (1 to 7000), there is 

 also growth. 



On agar at 37 C. the organism grows rapidly, producing thin, moist, translucent 

 creamy greyish-white colonies of irregular shape and size. The colonies grow more 

 rapidly on the surface than in the depth of the medium. The same appearances 

 occur on agar at 20 C. , except that the growth is delayed. Gas bubbles frequently 

 occur in the condensation fluid. 



Litmus lactose agar (2 per cent.) The medium is turned red in twenty-four hours, 



B. Typlwsus. . B. coli. 



FIG. 9. Diagrams of B. typhosus and B. coli. 



and the surface growth becomes tinged slightly with the reddened litmus. Numer- 

 ous gas bubbles are produced in the medium. 



On potato at 37 C. there is produced in twenty-four hours a thick, moist, 

 yellowish-grey growth, becoming brown in old cultures. The colour varies widely 

 in degree, sometimes being richer than at other times. The potato becomes changed 

 in colour near the growth. If the potato is not fresh, or its reaction has been made 

 alkaline, the growth of B. coli may be almost colourless. There are, of course, a 

 very large number of bacteria which produce a growth on potato not readily 

 distinguishable from B. coli. 



Litmus milk Usually an acid curdling of the milk occurs in twenty-four hours at 

 37 C., though sometimes slightly delayed. The bluish-purple colour changes to 

 pink, then the whole of the milk is turned into a solid compact coagulum, the milk 

 itself becoming white. Later the redness extends from the surface downwards 

 until the whole contents of the tube are bright red in colour. 



On blood serum at 37 C. an abundant white glistening layer is rapidly developed, 

 somewhat similar to the growth on agar. There is no liquefaction. 



water). The reaction 



-eight hours at 37 C., but in any case is generally 

 kept at 37 C. for five days. The "red reaction " 

 may be obtained by adding to such a culture 1 c.c. of a 0'02 per cent solution of 

 potassium nitrite, and 0'5 c.c. of strong sulphuric acid. If the colour (due to 



