CHAPTER XXXI. 

 SKIN INFECTIONS. 



CULTURAL methods are to be preferred in the bacteriological 

 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 in- 

 fections. 



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 bottle bacillus, which morphologically resembles a yeast, is 

 considered to be the cause of dry pityriasis 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 



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