330 



BACTERIA PATHOGENIC TO MAN 



FIG. 101 



Staphylococcus. X 1100 diameters. 



brown color, somewhat darker in the centre, and surrounded by a 

 smooth border. The colonies grow rapidly. The appearance of the 

 growth is most characteristic. Immediately surrounding the colonies, 

 which are of a pale-yellow color, there is a deepening of the surface of 

 the gelatin, due to its liquefaction. By suitable light a number of these 

 shallow depressions with sharply defined outlines may be seen on the 

 gelatin plate, having a diameter of from 5 to 10 mm., in the centres of 



which lie the yellow colonies. Later, the 

 liquefaction becomes general, the colonies 

 running together. In stab cultures in 

 gelatin a white confluent growth at first 

 appears along the line of puncture, followed 

 by liquefaction of the medium, which 

 rapidly extends to the sides of the test- 

 tube. At the end of two days the yellow 

 pigmentation begins to form, and this in- 

 creases in intensity for eight days. Finally, 

 the gelatin is completely liquefied, and the 

 staphylococci form a golden-yellow or 

 orange-colored deposit at the bottom of the 

 tube. Under unfavorable conditions the 

 Staphylococcus aureus gradually loses its ability to make pigment and 

 to liquefy gelatin. 



GROWTH ON AGAR. In streak and stab cultures on agar a whitish 

 growth is at first produced, and this at the end of a few days becomes a 

 faint to a rich golden-yellow on the surface. The yellow pigmentation 

 is produced only in the presence of oxygen ; colonies found at the bottom 

 of a stab culture or under a layer of oil remain white. 



MILK. Milk inoculated with this micrococcus is coagulated at the 

 end of from one to eight days. 



GROWTH ON POTATO. Upon this substance the staphylococci grow 

 readily and produce abundant pigment. 



GROWTH ON LOEFFLER'S SOLIDIFIED BLOOD SERUM. Growth vigor- 

 ous, with fairly good pigment production. Some varieties slowly liquefy 

 the serum. 



GROWTH ON BLOOD AGAR. If nutrient agar to which a little animal 

 blood has been added is streaked with staphylococci there appears, at 

 the end of twenty-four hours at 35 C., about the growth a clear zone, 

 owing to the hsemolytic effect of the Staphylococcus products. 



In certain culture media, as the result of the growth of the Staphylo- 

 coccus aureus, there is a production of acid in considerable quantities, 

 these consisting chiefly of lactic, butyric, and valerianic acids. These 

 acids have been supposed to play a part in the production of pus, in 

 which, according to some observers, they are often present. 



RESISTANCE. The Staphylococcus is distinguished from most other 

 pathogenic bacteria by its comparatively greater power of resistance 

 to outside influences, desiccation, etc., as well as to chemical disinfectants. 

 Cultures of the Staphylococcus pyogenes in gelatin or agar retain their 



