CULTIVATION 751 



bran, silage, cornmeal, and olive-juice ; by Mcintosh, James and Lazarus-Barlow 

 (1922, 1924) from carious teeth ; and by Kendall (1910) from sewage. Eggerth 

 and Gagnon (1933) and Eggerth (1935) drew attention to the presence in normal 

 adult faeces of Gram-positive and Gram-negative anaerobic bacilli, which they 

 described under the generic name of Bacteroides. There seems little doubt that 

 the Gram-positive members are closely related to the lactobacilli and they will 

 therefore be described in this chapter. 



Morphology. — The members of this group are in general fairly large, non-motile, 



non-sporing, Gram-positive bacilli. They are arranged singly, in pairs end-to-end, 

 in chains, and sometimes in palisades (Fig. 151). Some members are markedly 

 pleomorphic, especially in old cultures, forming clubbed, knobbed, curled, spiral, 

 candle-flame, vacuolated, whorled, and filamentous forms, and frequently showing 

 irregular, granular, or beaded staining. In some species the bacilli tend to be 

 arranged at angles to each other, giving rise to Y-forms, which may simulate true 

 branching. Another characteristic of some members is the formation of lateral 

 offshoots or buds, either directly adherent to the parent cell, or connected with it 

 by a short stem ; these buds may themselves be bifid. 



Cultivation. — These bacteria do not as a rule grow well on the usual laboratory 

 media ; their growth is much improved by the addition of whey or glucose. Surface 

 colonies show a good deal of variation, but on the whole conform to one or other 

 of the two types described by Mereshkowsky (1905, 1906) : (1) round or navicular, 

 pinhead in size, opaque, whitish, and surrounded by an areola of turbid agar ; 

 (2) round or irregularly round, less 

 than pinhead in size, greyish, trans- 

 lucent colonies with a finely erose - \ 

 edge, and with no areola around \ 

 them ; microscopically these col- " V ■ 

 onies are of typically rhizoid struc- **~* >^.i.^ 

 ture. Deep colonies in glucose ^ 

 agar likewise tend to be either ..^ 

 compact, with an entire edge or --.-,_—-' 



sometimes a single lateral knob .^— -^ .» '^ 



(Rettger and Morton's (1914) Y ^ -^^ ) "^ '(^'' 



type), or curled, rhizoid, and / /' - 



feathery, looking like a tuft of / / 



hair or moss (Rettger and Horton's / •'' ^ 



X type). Intermediate types of 

 colony are not uncommon. The 

 compact and feathery types of 



colony are referred to by some Fig. 151. — Doderlein's bacillus, 



writers as " smooth " and " rough " From an agar culture, 48 hours, 37° C. ( X 1000). 

 respectively, but since the par- 

 ticular type of colony formed seems to depend largely on environmental con- 

 ditions, and since there seems to be little relationship between the colonial 

 type and any other important characteristic of the organisms, it is probably 

 wiser to refrain from the use of terms that have now come to possess a wider con- 

 notation. A very characteristic appearance is the turbidity or milkiness of the 

 agar produced in shake plates or tubes ; it is a variable characteristic, however, 



