524 



SPECIAL PHYSIOLOGY. 



their own weight in one hour. When first secreted, and especially 

 during active secretion, the saliva is alkaline ; that of the submaxil- 

 lary gland is less so than that 'of the parotid. In fasting, the moisture 

 of the mouth is nearly neutral, or even acid, at that time consisting 

 probably almost entirely of mucus. The ptyalin or salivin, the most 

 important constituent of the saliva, is an albuminoid substance. Of 

 the salts, the tribasic phosphate of soda is probably the cause of the 

 alkalinity of the secretion; besides this, there are found chlorides of 

 sodium and potassium, sulphate of soda, phosphates of lime and mag- 

 nesia, and oxide of iron. The tartar of the teeth is formed by a de- 

 posit of these earthy salts, mixed with mucus, and the remains of 

 bacteria or vibrios; it contains 20 per cent, of animal matter. Urea 

 has also been found in the fluids of the mouth, and traces of ammonia, 

 the results of decomposition. Thus far. the salts of the healthy saliva 

 resemble those of the blood; but it contains a peculiar and remarkable 

 salt, named the sulphocyanide of potassium-, which strikes a deep red 

 color with a solution of a persalt of iron. 



Source and Composition of the Gastric Juice. 



When the soft pulpy mucous membrane of the stomach is examined 

 under a moderate magnifying power, it presents a delicate honeycomb 

 appearance (Fig. 93), caused by numerous shallow, hexagonal, or 

 polygonal, depressions, named the cells or alveoli of the stomach; 

 near the pylorus, these measure y^^h f an inch * n width, but else- 

 where are smaller and less distinct, measuring only 5 ^th to -gj^th of 

 an inch. Between the alveoli are slightly elevated ridges, upon 

 which, especially near the pyloric end of the stomach, are minute 

 processes, which somewhat resemble villi, and are more distinct in the 



Fig. 93. 



Fig. 94. 



Fig. 93. Minute portion of the surface of the mucous membrane of the human stomach, showing the 

 polygonal depressions or alveoli, with the elevated ridgea between them. At the bottom of the alveoli, 

 are seen the open mouths of clusters of the tubuli of the stomach, or gastric tubuli. Magnified 60 diame- 

 ters. (After Boyd.) 



Fig. 94. Perpendicular section through a small piece of the mucous membrane of the stomach, to show 

 the clusters of the gastric tubuli. . neck of a single tubule. 6, dilated end or fundus, filled with glaud- 

 ular epithelial colls, c, orifices of the tubuli, at the bottom of the alveoli, m, muscular bundles of the 

 muscular coat. (After Kolliker.) Magnified 40 times. 



infant. No lacteals, however, have been detected in them. At the 

 bottom of the alveoli are clusters of minute spots (Fig. 93), which are 

 the orifices of tubular follicles. These follicles, called the gastric 



