CHAPTER XII. 



MICROCOCCI. 



THESE organisms consist of cells more or less globular in 

 form and varying in size from 0-5 micron to 2 micra in 

 diameter, but most measure about I micron ( T ^Vir mm., or 

 ^sooo of an inch). They are usually classified according 

 to the mode of division or the resultant shape. Thus 

 we have streptococci, staphylococci, diplococci, tetracocci 

 (tetragenus), and sarcinae. None show endogenous spore 

 formation, but of some it is alleged that they form arthro- 

 spores. Most are non-motile, but a few motile species 

 possessing flagella have been described (none pathogenic). 



STAPHYLOCOCCI. 



These were first demonstrated in pus by Pasteur in 

 1880 and Ogston in 1881, and in pure culture by 

 Becker in 1883. Rosenbach in 1884 established specificity 

 as cause of some forms of wound-suppuration and of 

 osteomyelitis. They are so named from their growth in 

 grape-like clusters. Several hundred species have been 

 described, but the chief varieties are : Staphylococcus 

 pyogenes (aureus, albus, and citreus) ; Staphylococcus 

 epidermidis albus ; Staphylococcus cereus (albus and 

 flavus). 



The common characteristics are : Grape-like clusters of 

 cocci, 0-9 micron in diameter ; non-motile ; non-sporing ; 

 grow readily on most media ; stain readily ; Gram-positive ; 

 gelatin-liquefying ; produce acid and clot in milk ; form 

 indol ; reduce nitrates to nitrites ; show colour reduction 

 with litmus, methylene-blue, and rosanilin (fuchsin) ; 

 aerobes, but facultative anaerobes ; optimum temperature 

 for growth, 28 to 30 C. Range from 8 to 42 C. 

 Thermal death-point 30 min. at 80 C. ; 'freezing useless. 



Cultures. Put up (i) broth, (2) agar slope, (3) agar 



