DESCRIPTION OF SPECIES 



413 



stomach and other parts of patient 

 suffering from the disease. May 

 be present in healthy throats of 

 persons in proximity to diphtheria 

 patients. Generally somewhat 

 localised to membrane, but may 

 be found in blood and internal or- 

 gans. Secondarily, infects articles 

 of clothing, milk, etc. 



Morphology — Slightly curved rods 

 with one end commonly rounded 

 or club shaped, the opposite end 

 commonly pointed ; occasionally 

 in dumb-bell form ; polymorphism 

 in old cultures and in some media. 

 Escherich classifies diphtheria 

 bacilli into three main groups, (a) 

 short, wedge - shaped, comma- 

 shaped ; {b) long, slender, cylindri- 

 cal form ; (c) involution forms, 

 club shaped. The forms varj' how- 

 ever ver>' widely and irregularly, 

 especially in old cultures. Some 

 authorities hold that the wedge- 

 shaped and spindle forms are the 

 more virulent ; and the short ovoid 

 forms are less so. 1-2 to 2 /* long, 

 0-3 to 0-5 M broad. 



Manner of grouping — In cover-glass 

 preparation from typical and pure 

 culture the diphtheria bacilli may 

 occur singly but more commonly 

 in groups of two, three, or four, 

 parallel with each other or at 

 angles resembling a V or a circum- 

 flex accent. They never form 

 long chains. Frequently grouped 

 like cruciform characters or Chinese 

 letters. Paucity of interlacing and 

 club forms and predominance of 

 parallel forms points to the pres- 

 ence of pseudo-diphtheria bacillus 

 (Escherich). Crossing and inter- 

 lacing of the longer forms is 

 supposed to be due to a formation 

 of new bacilli by the outgrowth of 

 chromatic granules in a direction at 

 right angles to the parent bacillus 

 (Escherich, Neisser, Shattock, etc.). 



Staining reaction — Aniline dyes ; 

 Gram's method (if decolorising not 

 too prolonged) ; Loffler's stain 

 (brings out striped appearance) ; 

 NicoUe's stain. 



Capsule — Present ; no flagella ; non- 

 motile. 



Spore forynation — N one. 



Biology : cultural characters {includ- 

 ing bioche7nical features') — Grows 

 best at 37° C. 



Bouillon — Dust-like granules, a 

 cloud at foot of tube ; pellicle usually 

 present ; indol, acid, and nitrites 

 are produced. 



Gelatine plates and tubes — Slow 

 growth at temperature 22 to 24° C, 

 not characteristic, non-liquefying ; 

 surface growth yellowish-white, 

 and slightly elevated. 



Agar plates and tubes — Char- 

 acteristic growth in 24 hours, 

 circular, round, white elevated 

 colonies ; smooth border ; moist 

 appearance. Luxuriant growth in 

 glycerine-agar tubes. Growth not 

 so luxuriant as on blood serum ; the 

 pseudo-bacillus grows well on agar. 

 Potato — Upon acid potato little 

 or no growth ; upon alkaline potato 

 scanty veil-like growth in several 

 days. 



Milk — Abundant growth ; na 

 coagulation ; amphoteric reaction. 

 Blood serum (or Loffler's medium) 

 — Rapid growth at 37' C, char- 

 acteristic by twelfth hour (thus 

 getting the start of other organ- 

 isms) ; round, raised, greyish-white 

 colonies, wth a yellowish tinge, 

 translucent if very young ; surface 

 moist and margin irregular ; by 

 transmitted light the colonies show 

 an opaque and thickened centre ; 

 in older colonies this centre may 

 appear even more obvious. If the 

 colonies are few and widely separ- 

 ated they may grow to a consider- 

 able size (4 to 5 mm.), but if 



