DIGESTION. 



147 



physical development and activity be assumed to be 540 grams (19 oz.) of 

 the former and 450 grams (16 oz.) of the latter, these two substances would 

 absorb respectively 297 grams (4573-8 grains) and 216 grams (3326.4 grains), 

 making a total of 513 grams (7900 grains). If, therefore, the amount 

 secreted and mixed with the food during an estimated two hours of mastica- 

 tion be added to the amount secreted during the remaining twenty-two hours, 

 supposing that it continues at the rate of 36 grams per hour, we have a total 

 amount of 513+792 grams, or 1305 grams (19,780 grains), or about 2.8 

 pounds. 



Histologic Changes in the Salivary Glands during Secretion. 

 During and after secretion very remarkable changes take place in the cells 

 lining the acini, which are in some way connected with the production of the 

 essential constituents of the salivary fluids. In the case of the parotid gland, 

 which may be regarded as the type of a serous or albuminous gland, the 

 following changes have been observed by Langley (Fig. 65). During the 



FIG. 65. PAROTID GLAND APTER PRO- 

 LONGED ACTIVITY. 1,1, Acini; 2, duct; 3,3, 

 albuminous cells almost free of granules; 4, 

 nuclei clear and well denned. (Semi-diagram- 

 matic.) 



FlG. 66. SUBMAXILLARY GLAND AFTER 



PROLONGED ACTIVITY. 1,1, Acini; 2, duct; 

 3,3, mucous cells free of mucin and filled 

 with fine granules; 4,4, nuclei rounded and 

 returned to the center of the cell; 5,5, cells of 

 Giannuzzi, large and distinct. (After 

 Vialleton.) 



period of rest and just previous to secretor activity, the epithelial cells are 

 enlarged and swollen, and encroach on the lumen of the acinus. The 

 protoplasm of the cells is so completely filled with dark^fine granules as not 

 only to obscure the nucleus, but almost to obliterate the line of union of the 

 cells. As soon as secretion becomes active, however, the granules begin to 

 disappear from the outer region of the cell and move toward the inner border 

 and into the lumen of the acinus. From these observations it might be 

 inferred that during rest the protoplasm of the cells gives rise to granular 

 material, and that during and after secretor activity there is an absorption 

 of new material from the lymph and a reconstruction of the granular material. 

 In the submaxillary gland, a portion of which may be taken as a type of a 

 mucous gland, similar changes have been observed (Fig. 66). During rest 

 the epithelial cells are large, clear in appearance, highly refractive, and loaded 

 with small globules resembling mucin. The nucleus, surrounded by a small 

 quantity of protoplasm, lies near the margin of the cell. That the granules 

 are not protoplasmic in character is shown by the fact that they do not stain 



