162 SUPPURATION PUS COCCI. 



On gelatin plates small round granular colonies, with a 

 sharply defined border and a whitish-gray color, are seen to 

 develop within forty-eight hours. The gelatin is gradually 

 liquefied around these colonies. The colony is high in the 

 centre and gradually slopes down toward the periphery. It 

 is very thin at the edge. It resembles a small pile of sand. 

 After a few days the golden-yellow color appears, beginning 

 at the centre and gradually spreading toward the periphery. 

 The color is not so pronounced in plate colonies as in tube 

 cultures. The structure of these colonies is studied with the 

 low power of the microscope. 



On agar-agar plates the appearance of the colonies is simi- 

 lar to that of the colonies on the gelatin plates, but there is 

 no liquefaction of the medium and the pigment is more 

 intense. 



In the gelatin tube culture the growth occurs along the 

 entire length of the stab, with rapid liquefaction of the 

 medium in the form of an inverted cone. The culture gradu- 

 ally settles to the bottom of this cone, where pigment-forma- 

 tion is evident. The supernatant liquid is always cloudy but 

 not colored. Pigment-formation is not well marked in gel- 

 atin tube cultures. 



On agar stroke cultures pigment-formation appears early 

 and is very intense, beginning at the centre of the culture. 

 The growth is limited to the needle track, and is very heavy, 

 moist, and shining, with well-marked and quite regular 

 edges. At first the growth is white, but in a few days the 

 orange pigment begins to appear, especially if the tube is 

 kept in a light place, with a plentiful supply of oxygen. 



On potato the growth resembles that on agar, but it is not 

 limited to the line of inoculation. It frequently forms a 

 thick moist membrane that covers the entire surface of the 

 potato. The culture gives off a peculiar sour odor. 



Bouillon rapidly becomes clouded, but without the produc- 

 tion of pigment. 



Milk is coagulated, with the production of lactic and several 

 other acids. 



The production of the various pigments is not constant; 

 the staphylococci varying in this respect. The cultures may 



