pus. 149 



FALSE PUS. 



There are many substances and fluids having resemblance 

 to pus which are not really purulent ; thus, softened clots of 

 fibrin, which are so frequently encountered, especially in 

 phlebitis, bear the closest possible similitude to true pus in 

 general appearance, and yet in their intimate structure they 

 are totally dissimilar, as may be clearly determined by means 

 of the microscope. 



If a portion of softened fibrin be examined microscopically, 

 it will be found to be made up of a granular material, from 

 which pus corpuscles, or corpuscles similar to them, are either 

 entirely absent, or in which they occur but in very small 

 numbers : now, with true pus, the reverse is the case ; the 

 corpuscles are its chief and most conspicuous element. 



It is only by means of the microscope that the nature of 

 softened fibrin can be ascertained ; until within the last few 

 years it has always been mistaken for true pus, and the oc- 

 currence of masses of fibrin thus altered in the blood-vessels 

 has led to the opinion that the formation of pus in them is 

 not an unfrequent event. 



On the other hand, fluids are sometimes met with which 

 look very unlike proper pus, and which are yet found on ex- 

 amination to be veritable pus. These facts show the neces- 

 sity of a careful microscopic examination in all important and 

 doubtful cases. 



METASTATIC ABSCESSES. 



Another notion, the erroneousness of which has been ren- 

 dered manifest by means of the microscope, is that which has 

 been entertained in reference to the removal of an abscess 

 seated in one part of the body, and its subsequent deposition 

 in another situation. 



The knowledge of the existence of pus corpuscles in the 

 fluid of abscesses, and the fact that no channels exist by which 



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