240 PRACTICE OF PHYSIC. 



appearance of pus without ulceration in CCCXLIX : but, 

 after all, I cannot help suspecting the accuracy of his observa- 

 tions ; must entirely reject his explanation of them ; must 

 however allow, that we still want facts to support the explana- 

 tion I have offered ; and doubt much if it will apply to any 

 case of phthisis. For these reasons I still conclude, agreeably 

 to the faith of all other dissections, and the opinions of all 

 physicians, that the symptoms mentioned in our definition, de- 

 pend always upon an ulceration formed in the lungs. 



DCCCLVI. It has sometimes happened, that a catarrh was 

 attended with an expectoration of a matter so much resembling 

 pus, that physicians have been often uncertain whether it was 

 mucus or pus, and therefore whether the disease was a catarrh 

 or a phthisis. It is often ef consequence to determine these 

 questions ; and it appears to me that it may be generally done, 

 with sufficient certainty, from the following considerations, of 

 which each particular is not always singly decisive, but when 

 they are taken together can hardly deceive us. 



1. From the colour of the matter ; as mucus is naturally 

 transparent, and pus always opaque. When mucus becomes 

 opaque, as it sometimes does, it becomes white, yellow, or 

 greenish ; but the last mentioned colour is hardly ever so re- 

 markable in mucus as in pus. 



2. From the consistence ; as mucus is more viscid and co- 

 herent, and pus less so, and may be said to be more friable. 

 When mucus is thrown into water, it is not readily diffused, 

 but remains united in uniform and circular masses : but pus, 

 in the same circumstances, though not readily diffused, does 

 not remain so uniformly united, and by a little agitation, is 

 broken into ragged fragments. 



3. From the odour ; which is seldom perceived in mucus, 

 but frequently in pus. It has been proposed to try the odour 

 of the matter expectorated, by throwing it upon live coals : but in 

 such a trial both mucus and pus give out a disagreeable smell, 

 and it is not easy to distinguish between them. 



4. From the specific gravity compared with water ; and, in- 

 deed, it is usual for the mucus of the lungs to swim on the sur- 

 face of the water, and for pus to sink in it. But in this we 

 may sometimes be deceived; as pus which has entangled a 



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