386 THE SOLIDS. 



rupture of coagulable lymph through the walls of the vessels, 

 the consolidation of which in the air cells constitutes the con- 

 dition of the lung known by the name of hepatization : these 

 results are probably necessary consequences of the protracted 

 congestion : the third stage of pneumonia is attended by the 

 formation and excretion of granular cells in large quantities, 

 imbedded in a fibrinous fluid : the excreted matter may be 

 either mucus, constituting the stage of resolution, or it may 

 be pus, when the pneumonia is said to terminate in puru- 

 lent infiltration : the difference between the two excre- 

 tions is one of degree rather than of kind. With respect to 

 the nature and origin of the granular corpuscles, some phy- 

 siologists will have it that they are the white corpuscles of 

 the blood escaped from the vessels an opinion completely 

 untenable: they doubtless have an origin external to the 

 blood vessels, and are to be regarded as of an epithelial cha- 

 racter, representing as a rule the peculiar epithelium of the 

 surfaces or parts from which they emanate. 



Tubercle. The earlier microscopic observers approached 

 the investigation of tubercle, especially of tubercle in the 

 lungs, with the expectation of finding in tubercular matter 

 some peculiar element or structure which should account for 

 the fatality and apparent malignity of that fearful affection, 

 not knowing fully the true structure of the organs of respira- 

 tion, and therefore not perceiving clearly that this fatality is 

 occasioned rather by the peculiar structure of the lungs them- 

 selves, than by any malignity in the character of the tuber- 

 culous formation. Some of these observers have even fancied 

 that they have discovered in the matter of tubercle peculiar 

 and characteristic cells : it is now scarcely necessary to re- 

 mark, that careful and extended microscopic investigation 

 does not warrant any such conclusion. 



One of the most accurate views with which I am ac- 

 quainted respecting the nature of tubercle, is that put forth 

 by Dr. Addison.* 



" Tubercles of the lungs," he writes, " are composed of 



* Experimental Researches. Transactions of Provincial Medical, and 

 Surgical Association, vol. xi. pp. 287, 288. 



