393 



MODIFICATIONS IN FORM OF THE SECRETING SURFACE. 



It is generally assumed that the former is the case, and that the protoplasm of the 

 cells of a secreting gland increases in amount as the first stage in the process of 

 formation of the secretion. But since the materials of secretion accumulate in the 

 substance of the protoplasm, it may not be always possible to determine how much 

 of the increase of size of the cell is due to a growth of the protoplasm itself, and 

 how much to the accumulation of the materials of secretion, either entirely or only 

 partially elaborated, within it. 



The secretory changes which have been noticed by various observers in the cells- 

 of different glands, will be more fully described when the several glands are specially 

 treated of. 



Modifications in form of the secreting surface. A secreting apparatus 

 effectual for the purpose which it is destined to fulfil, may thus be said essentially 

 to consist of a layer of secreting cells covering a free surface, whilst a layer of finely, 

 ramified blood vessels is generally spread out close to the attached ends of the cells,, 

 with sometimes a basement membrane between the two. But whilst the structure- 

 may remain essentially the same, the configuration of the secreting surface presents 

 various modifications in different secreting organs. In some cases, the secreting 



Fig. 455. PLAN OF A SECRETING MEMBRANK. 

 (Sharpey.) 



a, membrana propria or basement-membrane ; 

 1>, epithelium, composed of secreting cells ; c, 

 layer of capillary blood-vessels. 



surface is plain, or, at least, expanded, as in various parts of the serous, synovia! 

 and mucous membranes, which may be looked on as examples of comparatively 

 simple forms of secreting apparatus ; but, in other instances, and particularly in the 

 special secretory organs named glands, the surface of the secreting membrane is 

 variously involved and complicated. An obvious effect of this complication is to 

 increase the extent of the secreting surface in a secreting organ within a given bulk, 

 and thus augment the quantity of secretion yielded by it. No connection has been 

 clearly shown to exist between the quality of the secretion and the particular con- 

 figuration, either internal or external, of the organ ; on the other hand, we know 

 that the same kind of secretion that is derived from a complex organ in one animal 

 may be produced by an apparatus of most simple form in another. 



There are two principal modes by which the surface of the membrane is so 

 increased in extent, namely, by rising or protruding in form of a prominent fold or 



Fig. 456. PLAN TO SHOW AUGMENTATION. 



OF SURFACE BY FORMATION OF PRO- 

 CESSES. (Sharpey.) 



a, b, c, as in preceding figure ; d, simple 

 and ef. branched or subdivided processes. 



some otherwise shaped projection (fig. 456, d, 0,/), or by retiring, in form of a recess 

 (fig. 457, A, ff , h). 



The first-mentioned mode of increase, or that by protrusion, is not the one which is 

 most generally followed in nature, still it is not without example, and, as instances, 

 may be cited the Haversian fringes of the synovial membranes and the urinary 

 organ of molluscs. In these cases, the membrane assumes the form of projecting- 

 folds, which, for the sake of further increase of surface, may be again plaited and 

 complicated, or cleft and fringed, at their borders (fig. 456, e,f). 



The augmentation of the secreting surface by recess'ion or inversion of the mem- 

 brane, in the form of a cavity, is, with few exceptions, that generally adopted in the 

 construction of secreting glands. If the recess is simple its blind termination, which 



