Digestion. 103 



The three salivas secreted have different physical pro- 

 perties. Parotid saliva is watery, clear, free from mucin, 

 but containing a small quantity of proteid. Submaxillary 

 saliva is clear, viscid, contains formed elements, and in 

 those animals the saliva of which is amylolytic it possesses 

 ptyalin. The sublingual is more viscid than the submaxil- 

 lary, and contains more formed elements and organic salts. 



Colin has observed certain peculiarities in the salivary 

 secretion of herbivora which deserve our careful attention. 

 He has discovered that the secretion from the parotids is 

 unilateral ; the gland on that side of the mouth on which the 

 horse is masticating secretes much more than on the opposite 

 side ; the parotid on the masticating side gives two or three 

 times as much as its fellow ; the submaxillary and sub- 

 lingual glands, on the other hand, secrete equally, no matter 

 on which side mastication is being performed. Further, 

 the parotids secrete during rumination, the unilateral 

 secretion still being maintained, whilst the submaxillary 

 and sublingual glands are during this process in a state of 

 rest. In a fasting horse the parotids are quiet, whilst in 

 the ox they are active ; and observations tend to show that 

 in both animals during fasting the mouth is kept moist 

 by secretions from the sublingual, palatine, and molar 

 glands. These latter glands of the mouth are extensively 

 developed in the horse, particularly the palatine and some 

 large glands close to the epiglottis ; their secretion is viscid. 



Neither the sight of food nor the introduction into the 

 mouth of sapid substances produce any effect over the 

 salivary secretion from the parotid of the horse. Sapid 

 substances, however, stimulate submaxillary secretion. 



The use of the saliva in the herbivora is essentially that 

 of allowing of perfect mastication and lubrication of the 

 anterior digestive tract, of stimulating the nerves of taste, 

 and in ruminants assisting in rumination ; according to 

 my observations on the horse it has no chemical action on the 

 starch of food. So intimately, however, is salivary secretion 

 associated with starch conversion, that it is not possible to 

 pass over without further notice the action produced on 



