CHAPTER XXXII. 

 SKIN INFECTIONS. 



CULTURAL methods are as a rule to be preferred in the bacterio- 

 logical examination of the skin. 



This is best done by washing the surface to be examined with soap and water, in 

 order to eliminate chance organisms which may have settled on the surface of the 

 skin in dust or as a result of contact with material containing them. Scrapings are 

 then made with a sterile dull scalpel, and this material is emulsified in a drop of 

 sterile water in the center of a Petri dish. A tube of melted agar at 42 C. is then 

 poured on the inoculated drop and, by mixing, the bacterial flora is distributed over 

 the entire surface of the plate. Of the colonies developing on such plates probably 

 80% will be found to be staphylococci, and of these the greater proportion will 

 be staphylococci showing white colonies. 



Occasionally the aureus or citreus may be isolated. 



Streptococci and colon bacilli are rarely found. 



The Staphylococcus pyogenes aureus is the organism usually isolated from 

 furuncles, circumscribed abscesses, and carbuncles. 



Streptococci are the organisms to be expected in phlegmonous infections. 



Cold abscesses, which are frequently due to tuberculous infection, are, as a rule, 

 sterile. 



Acne pustules may show staphylococci or the microbacillus of acne may be 

 present. 



The Bacillus acnes is a short broad bacillus often showing a beaded 

 appearance when stained by Gram's method. It is Gram positive 

 According to Hartwell it grows readily on glucose agar when cultivated 

 anaerobically (Wright's method). Colonies appear in four to five days. 



Sabouraud's medium for its culture is: Peptone 20 grams, glycerine 20 grams, 

 glacial acetic acid 5 drops, agar 15 grams and water 1000 c.c. The bottle bacillus, 

 which morphologically resembles a yeast, is considered to be the cause of dry pityri- 

 asis capitis. It may also be found in the comedones of children. 



In the tropics, an organism which at times produces lesions similar to impetigo 

 and again pemphigoid eruptions and at other times wide-spreading erysipelatous 

 conditions gives cultural characteristics similar to S. pyogenes aureus. It is probably 

 only a virulent aureus. It has been described under the name of Diplococcus pem- 

 phigi contagiosi. 



The Staphylococcus epidermidis albus, or stitch abscess coccus, is considered by 

 Sabouraud to be the cause of eczema seborrhoicum. 



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