94 



MANUAL OF HISTOLOGY 



Fig. 93. Detached cells of epider- 

 mis from the human skin. 



58. 



Now, as to the decay of animal cells, \ve find their destinies to be very 

 various. 



Firstly, the existence of a cell may terminate purely mechanically; it 

 may be rubbed or peeled off from its bed. Thus we see the superficial 

 scale-like cells of the epidermis becoming dry and hard, and losing their 

 nuclei; at the same time that their previously secure connections, by means 

 of a cementing substance, become loosened, allowing of their easy separa- 

 tion. The same is the case, also, with the nucleated surface cells of 

 certain laminated epithelia of mucous membranes, as, for instance, of 

 those of the mouth. Such a separation also takes place from some of the 

 more simple or even single-layered epithelial coatings, although not to 

 the same extent as was formerly supposed. Thus mucus carries off some 

 of the cells of the locality in which it is produced. 



This mode of destruction, however, is the most rare, the cell passing on 

 more frequently through changes in its con- 

 sistence and composition to decay. 



The most usual way, probably, in which 

 cells are destroyed, is that of solution of their 

 bodies, and in the case of those possessing 

 membranes, rupture of the latter, with escape 

 of the contents, and eventual liquefaction of 

 the nucleus, if such have been present. Jn 

 this manner it is that blood-corpuscles are 

 supposed to disappear, as also the cells which clothe the cavities of 

 glands, and those in which spermatozoa are developed. Digested in 

 the slightly alkaline fluids of the system, the matter of which the 

 dying cell is composed is often transformed into a substance resembling 

 if not identical with mucus. These occurrences, taking place in the 

 gradual decay of the cell, are of interest from another point of view, 



namely, from the fact of their having 

 been misinterpreted by the adherents of 

 the older theorists, who reversed the order 

 of things to the support of their own pecu- 

 liar view. 



We occasionally meet among the more 

 delicate epithelia with both modes of de- 

 cay side by side. Thus, of those cells of 

 the'intestine covered by a thickened border, 

 some are cast off, whilst others first undergo 

 decomposition with solution of the upper 

 part of the membrane of the cell and escape of the contents (fig. 94, a). 



Another change to which the body of the cell is liable, is into colloid 

 matter, a much more stable substance than mucin, which, in contra- 

 distinction to the latter, is not precipitated by acetic acid. The connective 

 tissue cells of the plexus choroidei, and the cellular elements of the thy- 

 roid gland, are specially subject to this degeneration. 



But, again, through far different chemical transformations, so to speak, 

 can the cell meet the destiny of all organic things, its dissolution being 

 at the same time hastened. There are usually two kinds of deposits of 

 foreign matter to be found in the bodies of cells, which may make the latter 

 incapable of further existence, and, curiously enough, of substances widely 



Fig. 94. Cylinder epithelium from the 

 human intestinal villi (after Schuhze). 

 6, normal cell ; a, another in process of 

 transformation into inucus. 



