32 MUCOUS SOFTENING. 



a wliitCj finely granular scum in proportion as the salt is dissolved. 

 To this property must also be ascribed the readiness with which 

 the so-called '^ casein pellicles" form on the surface of solutions 

 of albumen in alkalies, when these are evaporated ; casein, ac- 

 cording to the most recent researches, being identical with alkahne 

 albuminate. The production of this substance is, therefore, the 

 last step in a cyclic series of metamorphoses which begin with 

 the conversion of the casein of milk (lactation) into the albumen 

 of the blood (the material of which the cells, and the collagen and 

 chondrigen of the intercellular substances, is built up) ; these in 

 their turn passing into mucin, and so back again to casein. Phy- 

 siological chemistry can point to more than one series of this 

 kind. The albuminates may be converted into mucin directly, 

 without passing through the intermediate stage of gelatin-yield- 

 ing matter, as is proved by the development of mucin in the 

 epithelium cells of mucous membranes. The mucin stage, too, 

 may be omitted ; we saw this in the case of fatty degeneration, 

 when the protoplasm of the cells was transformed directly into a 

 substance soluble in alkaline fluids, which served to hold the oil 

 globules together. On the other hand the place of mucin in the 

 chemistry of softening may be taken by other albuminoid 

 bodies ; as, for instance, by pyin, which is developed, together 

 with mucin, during the purulent liquefaction of connective tissues. 

 The enigmatical albuminoid basis of colloid degeneration also 

 belongs to this series ; it will have to be considered separately. 



§ 40. In proceeding to discuss the morphology of mucous 

 softening, we are met by two leading problems. What are the 

 phenomena attending the disintegration of existing tissues ? 

 What new forms are produced by their metamorphosis ? 



To the first of these questions we find a definite, though per- 

 haps inadequate answer in the history of mucus-formation on 

 the surface of mucous membranes, and in that of the softening of 

 cartilage and bone. 



It is an established fact that the mucus which covers the 

 surface of our mucous membranes is produced on the spot by 

 epithelial cells. By adding a sufficiency of water to the detached 

 epithelia, the formation of large spherules of clear mucus in the 

 interior of the cells may actually be followed under the microscope ; 

 they push aside the other cell contents, together with the nucleus, 

 making them look like mere appendages ; they finally escape, 



