220 DIGESTIVE SYSTEM. 



duced by the action of the nervous system, and nervous 

 terminal ramifications have lately been discovered, penetrat- 

 ing the glandular epithelial element (Pfliiger). 



Many physiologists maintain that the nerves affect the 

 secretion of the saliva only by their function as vaso-motors. 

 The question of the vaso-motor nerves that cause dilatation of 

 the vessels (see p. 173) here again presents itself. The belief 

 is, however, constantly growing into favor, that the influence 

 of the nervous system on secretion bears directly on the glob- 

 ular elements of the secretory pouches or bags (culs de sac), but 

 we must add that Pfliiger's researches on the subject of the 

 termination of the nerves in the glands are by no means calcu- 

 lated to produce conviction: this histologist supposes that the 

 nerve branches terminate in the so-called glandular culs-de- 

 sac, preserving even here their central nerve substance (mye- 

 line) ; were this the case, it would bean exception to the general 

 rule, for, when a nervous filament approaches its real termina- 

 tion, it usually lays aside its myeline, retaining only its 

 axis-cylinder, and sheath of Schwann. This fact leads us to 

 suppose that Pfliiger did not discover the real terminations 

 of the secretory nerves. 



On the other hand, histologists have made great efforts to 

 observe the act of fusion of the globular elements of secretion 

 at the moment when this takes place, or at least to ascertain 

 what changes appear in the epithelium of the glands after 

 abundant secretion : Boll, Giarmuzzi, and more particularly 

 lleidenhain and Ranvier, devoted themselves to the study of 

 this subject. Giannuzzi discovered in the salivary cells peculiar 

 prolongations in the form of pedicles, which are bent round 

 in a curve, and joined on to the enveloping membrane : he 

 found also, in the glandular culs-de-sac, between the envel- 

 oping membrane and the salivary cells, properly so called, 

 these peculiar formations he calls' half-moons (or crescents) 

 being special cells, flattened in shape, and with one or two 

 nuclei (in course of proliferation). The purpose of these 

 elements is not known. Heidenhain has observed that we 

 find in a gland, after abundant secretion, in place of the 

 large salivary cells, some which are much smaller and quite 

 granular ; he supposes that the larger cells are destroyed in 

 order to form the substance to be secreted, that the remains 

 escape with the salivary fluid; that the small new elements 

 arise from Ginnnuzzi's crescents, and that these are in- 

 tended to take the place of the salivary globules which have 

 been destroyed. Ranvier states that after abundant becre- 



