196 WOUND INFECTION AND PYOGENIC BACTERIA 



from artificial cultures the organisms occur in large, irregular grape- 

 like masses. In pus, however, this seldom occurs; instead they are 

 generally found in small groups or pairs, double pairs (tetrads), or 

 sometimes short chains. This sometimes makes it impossible to decide 

 quickly whether the organism is a staphylococcus, a diplococcus, or 

 a streptococcus. Cultures, of course, will definitely identify the 

 organism. The staphylococci possess no flagella, and do not form 

 spores. 



Cultural and Biological Properties. Pyogenic staphylococci grow 

 on a great variety of artificial culture media. Their range of tem- 

 peratures is wide and lies between 9 and 42 C.; the optimum tem- 

 perature is at 24 to 28 C., not at blood temperature. They grow 

 both in the presence and absence of oxygen, and also in a hydrogen 

 atmosphere, but not in pure carbon dioxide or illuminating gas. The 

 reaction of the culture soil, like the temperature, may vary consider- 

 ably, but a slight alkalinity is most favorable to their growth. The 

 organisms multiply very rapidly in nutrient bouillon, and under 

 favorable conditions a tube inoculated in the ordinary manner may, 

 after twenty-four hours, contain 85,000,000 cocci per cubic centi- 

 meter. The bouillon soon becomes intensely clouded, sometimes a 

 slight pellicle develops on the surface, and a slimy sediment is always 

 formed at the bottom of the tube after a growth of several days. 

 The tubes have a strong smell of old starch paste. The organism 

 also grows well in Dunham's peptone water and in milk. The latter 

 shows coagulation sometimes after a few days, always after eight 

 days. In gelatin stab cultures the growth extends along the entire 

 stab, and after a few days liquefaction begins at the surface and pro- 

 gresses downward. On gelatin plates small yellow points -around 

 which the medium is liquefied appear after two days. On blood serum 

 and LoefHer's blood-serum mixture the growth liquefies the medium 

 very slowly, sometimes not at all. If fresh sterile blood, particularly 

 rabbit's blood, is added to a solid culture medium on which the 

 staphylococcus is subsequently grown, solution of the red blood cor- 

 puscles (i.e., hemolysis) occurs. Potatoes are a good culture medium 

 for the organism, which does not ferment sugar. 



Pigment formation requires the presence of oxygen. It is not well 

 marked in the presence of too much strong diffuse light, but shows 

 best when the cultures receive only little light and are kept at tem- 

 peratures between 20 to 22 C. 



The liquefying properties of the staphylococci depend upon the 

 secretion of a tryptic ferment. It is now claimed that the strong 

 ferment liquefying gelatin and the rather weak one liquefying blood 

 serum and egg-albumen are two distinct types. Hemolysis due to 

 the growth of the organism is caused by a hemolysin. Staphy- 

 lococci also produce a substance which is very injurious to the leu- 

 kocytes of the rabbit. This body has been called leukocidin, which 

 means killing white blood corpuscles. Several investigators claim 



