8 4 



MEDICAL BACTERIOLOGY 



Type G 2 . Same shape and size as G, solid uniform staining. When stained 

 with Loeffler's methylene blue, granular and barred forms of diphtheria bacilli 

 are occasionally polychromatic, the granules and bars having a reddish tint. 

 The metachromatic appearance is given as a characteristic of Westbrook's types 

 A, C, D, E, F and G. 



Growth. The diphtheria bacillus is aerobic and grows at temperatures be- 

 tween 2oC. and 42C., best at 37C. The most favorable media for its culti- 

 vation are veal broth and Loeffler's blood serum. 



Bouillon (preferably veal infusion) incubated at 37C. after 24 to 48 hours 

 shows a thin white film on the surface, later the growth precipitates to the bottom 

 leaving the fluid clear. 



Loeffler's blood serum on this medium, incubated at 37C. round, elevated 





N\ 





FIG. 17. FORMS OF B, DIPTHERI^: IN CULTURES ON LOFFLER'S SERUM. 



A, Characteristic clubbed and irregular shapes with irregular staining of the cell contents. 

 X noo. B, Irregular shapes with even staining. X 1000. (After Park and Williams.') 



pin-point, grayish-white colonies appear in 16 to 20 hours; they enlarge, some 

 attaining the size of a pin head or larger, others coalesce, forming an irregular 

 outlined grayish film in 24 to 48 hours. 



Some cultures have a moist appearance and some have a light yellow tint. 

 Several days after inoculation the organisms show marked involution and the 

 culture becomes dry and tends to die. 



Agar. On agar growth has the same appearance as on Loeffler's medium; 

 it occurs more slowly, is less abundant, more distinctly white and does not die 

 out as soon as on blood serum. 



Gelatin. A few pin-point white colonies develop along a stab; on the surface, 

 occasionally, small round white colonies appear. Gelatin is not liquefied. 



Milk. Growth in this medium neither sours nor coagulates it. 



Spores are not formed. Indol is not formed. Acid is formed from glycerin, 

 glucose, galactose and maltose. Gas is not formed. 



Resistance. The diphtheria bacillus is easily destroyed by heat in a moist 

 state, 6oC. for 15 minutes kills, but when dried, especially when enclosed in a 

 false membrane, an exposure of i hour at i2oC. in a hot-air sterilizer is required 



