144 ORGANISED FLUIDS. 



it may not, in cases of suspected phthisis, in which sputa are 

 present. Now it is in cases of this description that we recog- 

 nise the importance of the discrimination of these substances, 

 and it is precisely in these and similar instances that the 

 microscope utterly fails us, for the want of an ascertained and 

 tangible difference in the two fluids submitted to the test of 

 its powers. 



Even the most marked physical qualities of pus, such as 

 its opacity and tenuity, may all be effaced by the employ- 

 ment of certain reagents, and converted into those which are 

 characteristic of mucus, thus pus, by the addition to it of 

 liquor potassa or of ammonia, is rendered transparent, and is 

 transformed into a thick and tenacious substance, resembling 

 mucus closely. This singular fact has been noticed by both 

 Addison and Donne, and on it the former clever observer has 

 built a theory remarkable for its ingenuity, but which is 

 here, nevertheless, deemed to be incorrect. 



The change of pus from an opaque substance to a trans- 

 parent one doubtless results from the solution of the pus 

 corpuscles, and to the presence of which the colour and 

 opacity of pus is due ; of the increased density and tenacity 

 of the pus thus treated it is less easy to afford a satisfactory 

 explanation. 



Addison thus accounts for it : the mucus and pus globules, 

 he says, contain filaments embedded in a fluid; these the 

 liquor potassa sets free by dissolving the envelopes of the cor- 

 puscles, and it is upon these filaments that the tenacity of 

 mucus, and of pus so acted upon, depends. Mr. Addison, 

 however, carries his reasoning upon the fact of the conversion 

 of pus into a fibrillating substance similar to mucus still 

 further. The white corpuscles of the blood, he states, also 

 contain fibres, and that these corpuscles, immediately on 

 their abstraction from the system, burst, giving issue to the 

 contained filaments. 



These filaments, he conceives, to constitute the fibrin of the 

 blood, which he declares does not exist in that fluid as fibrin, 

 but is only liberated from the corpuscles after the abstraction 

 of the blood from the system. . 



