Micrococcus Tetragenus 329 



in diameter. In cultures they do not show the regular arrange- 

 ment in tetrads as constantly as in the blood and tissues of animals, 

 where they occur in groups of four surrounded by a transparent 

 gelatinous capsule. 



Staining. — The organisms stain well by ordinary methods and 

 beautifully by Gram's method, by which they can best be demon- 

 strated in tissues. 



Isolation. — The organism can be isolated by inoculating a white 

 mouse with sputum or pus containing it, and after death recovering 

 it from the blood. 



Cultivation. — It grows readily upon artificial media. At temper- 

 atures ranging from i2°C. to 45°C., the optimum being 37°C. 



Colonies. — Upon gelatin plates small white colonies are produced 

 in from twenty-four to forty-eight hours. Under the microscope 



Fig. log. — Micrococcus tetragenus; colony twenty-four hours old upon the 

 surface of an agar-agar plate. X loo (Heim). 



they appear spheric or elongate (lemon shaped), finely granular, and 

 lobulated like a raspberry or mulberry. When superficial they are 

 white and elevated, i to 2 mm. in diameter. 



Gelatin. — In gelatin punctures a large white surface growth 

 takes place, but development in the puncture is very scant, the 

 small spheric colonies usually remaining isolated. The gelatin is 

 not liquefied. 



Agar-agar. — ^Upon agar-agar spheric white colonies are produced. 

 They may remain discrete or become confluent. 



Potato.— Upon potato a luxuriant, thick, white growth is formed. 



Bouillon. — A uniform clouding of the medium takes place. Acid 

 but no gas is produced when dextrose, lactose, saccharose and 

 mannite are added. 



Milk. — The milk is not changed in appearance and is not coagu- 

 lated. Litmus milk is shghtly acidulated. 



Blood-serum. — The growth upon blood-serum is also abundant, 



