PUS. 143 



when all other means have failed, he can occasionally arrive 

 at a tolerably accurate conclusion, but it is conceived that his 

 powers in this respect are also limited. 



Now the physical and chemical difficulties encountered in 

 the endeavour to discriminate pus from mucus arise, in all 

 probability, from the same cause which rendered it micros- 

 copically impossible so to do, viz. that no constant or essen- 

 tial difference does really belong to these fluids, whereby at 

 all times they may be characterised. 



Normal mucus and pus may be contrasted as follows : 

 Mucus is a thick, tenacious, and transparent substance, 

 easily admitting of being drawn out into threads, not readily 

 miscible with water, in which it floats, not so much from its 

 less specific gravity as from the circumstance of its great 

 tenacity, allowing it to retain in its substance numerous air 

 globules, which thus render it specifically lighter than the 

 water : it exhibits sometimes an acid, and sometimes an alka- 

 line reaction, according to the nature of the surface from 

 which it proceeds ; and it contains imbedded in its substance 

 solid particles of two forms, globules and scales : the former 

 are present in alkaline mucus, the latter in that which mani- 

 fests an acid reaction. 



Pus, on the contrary, is a thick, opaque, somewhat oily 

 substance, which does not admit of being drawn out into 

 threads, is readily miscible with water, in which it sinks ; its 

 chemical reaction varies, being sometimes alkaline, at others 

 acid : the solid particles which it contains are mostly of one 

 kind, globules : these are always very abundant, and float 

 freely in the fluid portion of the pus, while in that of mucus 

 they are unable to do so on account of its tenacity. 



Healthy mucus and pus, when thus contrasted, may fre- 

 quently be distinguished from each other, but it is in un- 

 healthy conditions of these two fluids, and especially when 

 they occur mixed together in variable proportions, that the 

 difficulty of discrimination is felt, and that the want of a 

 certain and positive character, whereby the diagnosis may be 

 always established, is experienced. 



This mixture of mucus and pus may actually exist, or 



