386 PATHOGENIC MICROORGANISMS 



infusion products. The optimum temperature for staphylococcus 

 cultivation lies at or about 35 C., though growth readily takes place 

 at temperatures as low as 15 C., and as high as 40 C. Slow but 

 denfiite growth has been observed at a temperature as low as 10 C. 



While development is most characteristic and luxuriant under 

 aerobic conditions, staphylococci are facultatively anaerobic on suit- 

 able media. They grow readily in an atmosphere of hydrogen. 



As to the reaction of media, staphylococcus develops most favor- 

 ably upon those having a slightly alkalin titer. Moderately in- 

 creased alkalinity or even moderate acidity of media does not inhibit 

 growth. 



On gelatin plates, growth occurs readily at room temperature, 

 forming within thirty-six to forty-eight hours, small, shining, pin-head 

 shaped colonies, appearing, at first, grayish-white, and later assuming 

 a yellowish hue, which intensifies into a light brown and often a bronze 

 color as the colony grows older. The intensity of the color differs con- 

 siderably in different races of staphylococci. Liquefaction of the 

 gelatin occurs, and, shallow, saucer-shaped depressions are formed 

 about the colonies after forty-eight hours or more. These zones of 

 fiuidification grow larger as the colonies grow, finally becoming con- 

 fluent. Microscopically, the colonies themselves, before liquefaction 

 has destroyed their outline, are round, rather finely granular, with 

 smooth edges. They are not flat, but rise from the surface of the 

 medium as the segment of a sphere. In gelatin stab cultures in tubes, 

 fluidification leads to the formation of a funnel-shaped depression, 

 with, finally, complete liquefaction of the medium and sedimentation 

 of the bacteria. Liquefaction of gelatin by the staphylococcus is due 

 to a ferment-like body elaborated by it, which is spoken of as "gela- 

 tinasQ. ' ' This substance can be obtained apart from the cocci by 

 the filtration of cultures. 3 It is an extremely thermolabile body. 



On agar plates the characteristics of the growth, barring liquefac- 

 tion, are much like those on gelatin. Colonies do not show a tendency 

 toward confluence, remaining discrete, and show a rather remarkable 

 difference in the size of the colonies occurring upon the same plate. 

 Upon slanted agar in tubes, rapid growth occurs, at first grayish-white, 

 but soon covering the surface of the slant as a glistening, golden-brown 

 layer. 



In broth, growth is rapid, leading to a general, even clouding of 



*Loeb, Cent. f. Bakt., xxxii, 1902. 



