CYSTS. 87 



tlie characters of a cyst due to softening. It will do this more 

 especially when it is shut off by a smooth and sharp boundary- 

 line. That such limitation of a cyst due to softening is not 

 brought about by any membrane capable of being anatomically 

 isolated, lies in the very nature of the thing. The presence of 

 such a membrane may very well be simulated, however, by all 

 the textural elements situated on the confines of the affected 

 region being in the same stage of metamorphosis, and thus 

 forming a layer which differs equally from the healthy paren- 

 cln-ma and from the fluid products of softening. 



So long as one of these cysts continues to enlarge by the 

 extension of softening to surrounding parts — so long, in a word, 

 as it remains a mere "centre of softening" (Erweichungsheerd), 

 it has no true limitary membrane. But a cyst originally due to 

 softening may subsequently obtain a lining membrane. In a 

 case of this sort, the softening process comes to a standstill, and 

 the adjacent tissues are organically marked off from the softened 

 part. Like all interstitial cavities in the parenchyma of the body 

 (whether physiological or morbid), the cyst is lined by a con- 

 tinuous layer of connective tissue, which may, under certain 

 conditions, become coated with epithelium. It is then analogous 

 in all respects to a bursa mucosa. Any changes which the con- 

 tents of the cyst may subsequently undergo depend on their 

 relations with the blood-vessels ramifying in the lining membrane : 

 should they increase in amount, their increase is due to exuda- 

 tion from the blood. The cyst due to softening may thus become 

 a secreting cyst. 



In conclusion, let me repeat what I have said already in the 

 course of the foregoing pages, that for the history of morbid 

 growths retention-cysts are of prime importance ; next come the 

 cysts due to softening and the hoamorrhagic cysts ; while the 

 exudation-cysts have next to no connexion with the subject. In 

 the nomenclature of morbid growths we usually employ the 

 prefix cysto^ to denote that they are complicated with cysts ; thus 

 Ave speak of cystosarcoma, cystocarcinoma, &c. 



2. On Normal as a Type of Morbid Growth. 



§ 71. The preliminary observations of a general character 

 contained in the foregoing sections have brought us to a point 



