CHAPTER VII. 



PYOGENIC ORGANISMS. 



Pus formation is not necessarily due to bacteria — Organisms of pus — 

 Staphylococcus pyogenes aureus — Methods of staioiag and growth 

 on media — Pathogenesis — Streptococcus pyogenes — Staphylococcus 

 pyogenes albus — Staphylococcus epidermid/is alhus — Staphylococcus 

 pyogenes citreus — Staphylococcus cereus a/wreus — Staphylococcus 

 cereus alhus — Bacillus pyocya/neus. 



In dealing with the organisms of pus, we shall describe only 

 those of common occurrence, and which are supposed tO' 

 give rise to pus formation, omitting those whose presence 

 is probably accidental. The formation of pus is not of 

 necessity dependent on the action of any micro-organism at 

 all, for pus may be entirely sterile ; the term aseptic pus 

 has been applied to such purulent discharges. It has been 

 shown experimentally that pus may be produced by the 

 introduction into the tissues of sterilised bacteria of several 

 kinds, the organisms alone being introduced without the 

 soluble products of their growth, so that the exciting cause 

 must be either the intracellular contents of the bacilli, or 

 possibly the mechanical effect combined with the positive 

 ' chemiotaxis ' that most bacteria exhibit to the leucocytes. 

 Certain other substances have been proved on injection to 

 cause the formation of pus, such as solutions of nitrate of 

 silver, strong ammonia, turpentine, etc. 



A large number of micro-organisms give rise to the 

 formation of pus, among which may be mentioned the 



