DIGESTION IN THE MOUTH 751 



administration of atropin, stimulation of this nerve produces, as 

 might be anticipated, an increased volume of the gland in consequence 

 of the dilatation of its vessels (Fig. 324). If, however, the gland be 

 allowed to secrete we obtain, in spite of the simultaneous increase 

 in size of the vessels, an actual diminution in the size of the gland 

 itself, showing that the first effect of the stimulation is on the cells of 

 the alveoli (Fig. 325). Under the stimulus these empty themselves of 

 the fluid they contain, replenishing their loss at the expense of the 

 fluid in the lymph spaces. The 

 increased passage of fluid from 

 blood to lymph space is there- 

 fore a secondary and not a 

 primary effect of the nerve 

 stimulation, and the first effect 

 on the gland is a diminution 

 of volume and not an increase, 

 as one would expect if the 

 vascular endothelium were 

 primarily responsible for the FIG. 326. 

 act of secretion. 



Mucous cells from a fresh sub- 

 maxillary gland of a dog. (LANGLEY.) 



a, mucous cell examined fresh from a 

 resting gland; a', the same cell treated 

 with weak alcohol ; b and &', cells from a 

 discharged gland before and after treatment 

 with weak alcohol. 



HISTOLOGICAL CHANGES 



DURING SECRETION 

 The process of secretion is 

 associated with marked changes 

 in the structure of the cells com- 

 posing the secretory alveoli. 

 The changes are of the same 

 general character whatever 

 class of glands we investigate, 



though the ease with which FIG. 327. Acini of a serous salivary gland. 



j ,n (LANGLEY.) 



they are to be demonstrated ^ ^.^ ^.^ . ^ discharged con . 



varies with the reactions of the dition. 

 various glands to the hardening 



fluids usually employed. If a small fragment of a mucous gland 

 be teased in blood serum or in 2 per cent. NaCl solution, the cells 

 are found to be packed with a mass of coarse highly refractive 

 granules (Fig. 326). If a corresponding specimen be made from 

 a serous gland (Fig. 327) the cells are also packed with granules, 

 which, however, are much finer in structure. On making similar 

 specimens from glands which have been forced to secrete for six or 

 seven hours, the individual cells are found to be much smaller and 

 the protoplasm of the cell is absolutely or relatively increased in 

 amount, while the granules are much fewer and are now confined 



