58 STUDY AND IDENTIFICATION OF BACTERIA 



2. Divide irregularly. Bunch of grapes arrangement. (Staphylococci.) 

 (fl) Gelatin not liquefied. M. cereus albus. 



(6) Gelatin liquefied. ( "' (Staphytococcu.) pyogenes albus. 



( M. (Staphylococcus) pyogenes aureus. 

 (c) Gelatin very slightly liquefied. 



S. epidermidis albus. (Stitch coccus.) 

 B. Cocci biscuit-shape. 



Diplococcus crassus. (May be mistaken for Meningococcus.) 

 On ordinary agar we have a scanty growth resembling the Streptococcus. Colo- 

 nies on ascites agar are smaller than those of Meningococcus. It produces acid in 

 glucose, maltose, lactose and saccharose. 

 II. Gram-negative cocci. 



only at about incubator temperature. 



1. Grow only on blood or serum media. Gonococcus. 



2. Grow on blood-serum media, or glycerine agar. 



(a) Diplococcus intracellularis_rneningitidis. Produces acid in glucose 



and maltose but not in lactose nor saccharose. 

 \^. Grows on ordinary media. Micrococcusjnelitensis. 

 B. will grow at room temperature as well as at 37C. 



(a) Micrococcus catarrhalis. Does noj: produce acid in glucose, maltose, 

 lactose nor saccharose. ^ 



(b) M. pharyngis siccus. Colonies dry and tough and adhere to medium. 

 NOTE. Other biscuit-shaped Gram-negative organisms resembling the Meningo- 

 coccus are (a) Diplococcus flavus. The colonies show yellow pigment and we have 

 three varieties according to the depth of the yellow color, (b} M. pharyngis siccus, 

 with yellowish, dry tenacious colonies and (c) M. cinereus with coarse dry colonies 

 on ascitic agar. Like M . catarrhalis, it does not ferment any of the above-mentioned 

 sugars. The individual cocci, however, are larger and more oblong in shape. 



STREPTOCOCCUS FORMS 



Those cocci tending to arrange themselves in chains are usually 

 described as streptococci. (Ogston, 1881; Rosenbach, 1884.) 



When we consider that certain bacilli at times assume an arrange- 

 ment which we term streptobacilli, yet have no relationship, it would 

 suggest that the matter of chain morphology is simply a characteristic 

 common to many entirely different cocci. 



Again old laboratory cultures of streptococci may show alternations of cocci and 

 rods giving the appearance of the dots and dashes of the Morse code. Furthermore 

 unsuitable media may bring about various involution types in an organism pri- 

 marily streptococcal. 



It is often difficult to distinguish streptobacilli from streptococci morphologically 

 and the same is true of diplococci and diplobacilli. These bacillary pairs and chains, 

 however, often show bipolar staining and are almost invariably Gram-negative. 



While streptococci tend to assume chain formation in pus and tissues they often 

 appear as diplococci in blood. 



