278 SPECIFIC MICRO-ORGANISMS 



but not always it is less virulent. Staph, epidermidis (Welch) is 

 an avirulent variety of Staph, alhus, very abundant on the normal 

 skin. Many other varieties of staphylococci have been described. 



Micrococcus Tetragenus. — This organism occurs in lung cav- 

 ities in phthisis, and in the sputum, usually in groups of four 

 cells, tetrads, enclosed in a transparent capsule. It is Gram- 

 positive, grows on ordinary media arid does not liquefy gelatin. 

 White mice and guinea-pigs are susceptible- and ordinarily die 

 of general bacteremia in two to six days after inoculation. The 

 pathogenic role of the organism in man is doubtful. 



Sarcina Ventriculi. — Goodsir in 1842 observed sarcines* in 

 vomitus. The coccus is large, 2.5/i in diameter, and occurs in 

 cubes of eight cells or as large conglomerates of these. It grows 

 on ordinary media, usually producing a yellow pigment. It 

 is found in the stomach in some conditions in which the acidity 

 of the gastric juice is diminished. It is apparently non-patho- 

 genic. 



Sarcina Aurantiaca. — This is a common saprophytic coccus 

 found in fermenting liquids and occasionally in the air. It 

 grows well on ordinary media and liquefies gelatin. An orange 

 pigment is produced. Typical packets are produced in liquid 

 media, especially in hay infusions. 



Micrococcus (Planococcus) Agilis. — This oganism occurs in 

 surface waters. It liquefies gelatin and produces a rose-red 

 pigment on agar and potato. Its remarkable feature is the pos- 

 session of a flagellum and active motility. It is Gram-positive. 



