162 TEXT-BOOK OF PHYSIOLOGY. 



Water constitutes the main ingredient, amounting to 99.5 per cent. 

 The soluble organic matter is proteid in character and is a mixture 

 of mucin, globulin, and serum-albumin. The potassium sulpho- 

 cyanid is mainly derived from the parotid gland. Its presence can be 

 demonstrated by the addition of a few minims of a dilute solution of 

 slightly acidulated ferric chlorid, when a characteristic red color is 

 developed. The inorganic constituents comprise the sodium, calcium 

 and ^magnesium phosphates, sodium carbonate, sodium and potas- 

 sium chlorids. 



Quantity of Saliva. The estimation of the total quantity of 

 mixed saliva secreted in twenty- four hours is exceedingly difficult, and 

 the results obtained must be only approximative. It is, of course, 

 subject to considerable variation, depending upon habit, the nature of 

 the food, etc. The experiments of Professor Dalton and the results 

 obtained by him are eminently trustworthy, and in all probability 

 represent as nearly as possible the exact amount secreted. He found 

 that without any artificial stimulus he was enabled to collect from 

 the mouth about 36 grams (540 grains) of saliva per hour, but that 

 upon the introduction of any stimulating substance into the mouth the 

 quantity could be greatly increased. During mastication the saliva 

 was poured out in greater abundance, the amount depending upon 

 the relative dryness of the food. He found that wheaten bread ab- 

 sorbed 55 per cent, of its weight, and fresh cooked meat 48 per cent. 

 If, therefore, the average quantity of bread and meat required daily 

 by a man of ordinary 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 mastication 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^pr about 2.8 pounds.N^ 



HistbTOgKPtSfingSrarthe 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 period of rest and just previous to 

 secretory activity, the epithelial cells are enlarged and swollen, and 

 encroach on the lumen of the acinus. The protoplasm of the cells 

 is so completely rilled with dark fine granules as not only to obscure 

 the nucleus, but to almost obliterate the line of union of the cells. 



