DIGESTION 149 



alkaline. It may, however, be neutral or even acid in reaction if there is 

 any fermentation of food particles in the mouth or in certain disorders of the 

 alimentary canal. When examined with the microscope, the saliva is seen 

 to contain epithelial cells, salivary corpuscles resembling leukocytes, particles 

 of food, and various microorganisms, especially Leptothrix buccalis. 



The chemic composition of the saliva is shown in the following table: 



COMPOSITION OF HUMAN SALIVA. 



Water 995 .16 



Epithelium i .62 



Soluble organic matter . . 1 .34 



Potassium sulphocyanid o .06 



Inorganic salts i .82 



1000.00 1000 04 



(Jacubowitsch.) (Hammer backer.) 



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

 The soluble organic matter is protein in character and is a mixture of 

 mucin, globulin, "and serum-albumin. The potassium sulphocyanid is 

 mainly derived from the parotid gland. Its presence can. be demon- 

 strated 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, and sodium and potassium chlorids. 



The relative amounts of the different constituents of the saliva will depend 

 on the relative degree of activity of the different glands, and this in turn will 

 be determined by the character of the food. When the food is dry, there 

 will be an excess of the parotid secretion; when it partakes of the consistence 

 of meat, there will be a larger secretion of the submaxillary saliva. The 

 glands apparently adapt their activity to the character of the food. 



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 consider- 

 able variation, depending upon habit, the nature of the food, etc. The 

 experiments of Professor Dalton and the results obtained by him are emi- 

 nently 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 wheat bread absorbed 

 55 per cent, of its weight, and fresh cooked meat 48 pei 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, suppos- 

 ing 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. 



