246 MANUAL OF BACTERIOLOGY. 



cause of suppuration than the staphylococcus pyogenes 

 aureus. It has, however, been found in acute abscesses on 

 numerous occasions. 



Staphylococcus epidermidis albus. According to Welch, 

 the epidermis of man contains with great regularity the 

 organism to which he gave the above name, and which he 

 considers to be a variety of staphylococcus pyogenes albus. 

 It grows, liquefies gelatin, and coagulates milk more slowly 

 than the ordinary staphylococcus pyogenes albus. It is, 

 furthermore, possessed of less marked pus-producing ten- 

 dencies. Welch found it impossible to sterilize the skin so 

 as to remove this micrococcus from it. The organism is 

 usually innocuous. It has been found in healthy wounds 

 on numerous occasions. It is capable of causing trouble 

 in wounds when necrotic or strangulated tissues are present, 

 or where a foreign body like a drainage-tube has been left 

 in the wound. It is a common cause of stitch abscesses. 



Streptococcus pyogenes. Appears as micrococci ar- 

 ranged in chains, often in pairs, when the adjacent cocci 

 may be flattened. Sometimes the chains are very long. 

 The diameters of the cocci vary from .4 to i //. Attempts 

 have been made to create varieties of streptococci accord- 

 ing to the length of the chains. On that basis a strepto- 

 coccus brevis and a streptococcus longus have been de- 

 scribed. 



The streptococcus pyogenes is not motile. It stains by 

 Gram's method. By the method of Hiss (page 57) capsules 

 may sometimes be demonstrated. It is facultative anaero- 

 bic; grows best in the incubator; more slowly at room tem- 

 perature, and does not liquefy gelatin. In gelatin plates it 

 produces small, round, white, punctiform colonies which are 

 slow of development, and are only visible after about three 

 days. It grows on the ordinary media; with the exception 

 of potato, according to some authors. Milk may or may not 



