632 THE MICROCOCCUS TETRAGENUS 



SECTION II. MORPHOLOGY. 

 1. Microscopical appearance. 



In sputum, pus and blood the Microccccus tetragenus appears as single 

 cocci, diplococci or as tetrads. The individual cocci are large, often exceeding 

 1/x in diameter ; they are sometimes oval and shaped like an haricot bean ; 

 and are frequently surrounded by an irregular capsule. 



^ In cultures on ordinary media the organism 



'*;. ' grows as single cocci or as diplococci, the diameter 



K seldom exceeding 0* 6-0' 7/x; the tetrad form is rarely 



:v.. ;:$ '' seen under these conditions, and capsules cannot 



. .v* * " be found. In cultures on liquid rabbit serum the 



''.. , ; ' ' tetrad forms with capsules can be demonstrated. 

 * ':::. ::* ... Staining reactions. The micrococcus is easily 



:i \\' f l stained by the ordinary methods and is gram- 

 * .. ., positive. Capsules may be stained in the usual 



way but are often poorly defined and irregular. 



: 



FIG. ^.-Micrococcus tetm- *' Cultural characteristics. 



f^lX^^S^efch 1 ) 111 ^ 6 ' Tte Micrococcus tetragenus grows on the ordinary 

 media at temperatures above 15 C. : at 20 C. 

 growth is slow : the optimum temperature is about 37 C. It is aerobic. 



Culture media. Broth. At first the medium becomes slightly cloudy but 

 as growth proceeds a thick ropy deposit is formed. 



Gelatin. Gelatin is not liquefied. Single colonies grow as 

 small convex white points 1-2 mm. in diameter. 



Stab cultures give rise to small isolated white colonies in 

 the depth of the medium and a white heaped-up growth on 

 the surface (tylotate growth). 



Chauffard and Ramond have described a strain of the coccus 

 which liquefies gelatin to a slight extent. Chromogenic varieties 

 also exist, viz. : M. t. aureus, M. t. subflavus and M . t. ruber. 



Agar. On this medium growth appears as white colonies 

 which become confluent and form a creamy white viscous 

 layer. 



Potato. Rounded colonies appear which coalesce and form 

 a white viscous layer. 



Liquid rabbit serum. The medium becomes cloudy and a 

 whitish deposit consisting of capsulated organisms is pre- 

 cipitated. 



Milk. The organism grows feebly in milk and does not 

 coagulate the medium. 



SECTION HI. BIOLOGICAL PROPERTIES. 



Viability. The organism remains alive in culture media for 

 several months. A temperature of 60 C. for a few minutes st f b , . culture 

 is sufficient to sterilize it. 



The virulence varies much with different strains ; virulent strains retain 

 their properties in culture almost indefinitely. 



Relying chiefly on differences in virulence some observers have described several 

 varieties of the micrococcus (M. t. septicus, M. t. variaUlis M. t. concentricus, M. t. 



