I /O DIGESTION 



tribute to the production of the saliva. The liquid that becomes more or 

 less thoroughly incorporated with the food before it reaches the stomach, 

 which must be regarded as the digestive fluid of the mouth, is known as 

 the mixed saliva ; but the study of the composition and properties of 

 this as a whole should be prefaced with a consideration of the different 

 secretions of which it is composed. The salivary glands belong to the 

 variety of glands called racemose ; and they resemble in their general 

 characters the other glands belonging to this class. One peculiarity, 

 however, in the histology of the secreting alveoli, may be mentioned : 

 Next the basement-membrane, usually near the blind extremity of the 

 tube, are a few crescentic cells called demilunes (Giannuzzi's crescents). 

 In the case of the submaxillary and sublingual glands, at least, these 

 bodies are thought to produce a serous secretion (see Plate IV, 

 Fig. i). 



Parotid Saliva. The parotid is the largest of the three salivary 

 glands. It is situated below and in front of the ear and opens by the 

 duct of Steno into the mouth, at about the middle of the cheek, opposite 

 the second large molar tooth of the upper jaw. The secretion of this 

 gland possesses little or no viscidity. 



, The organic matter of the parotid saliva is coagulable by heat 

 (212 Fahr., or 100 C), alcohol or the strong mineral acids. The se- 

 cretion is not so strongly alkaline as the submaxillary and the sublingual 

 saliva and contains a larger proportion of ptyalin. A sulphocyanate 

 is a nearly constant constituent of the parotid saliva. This can not 

 be recognized by the ordinary tests in the fresh saliva taken from the 

 duct of Steno, but in the clear filtered liquid that passes after the pre- 

 cipitation of organic matters, there is a distinct red color on the addi- 

 tion of ferric sulphate. As this reaction is more marked in the mixed 

 saliva, the methods by which the presence of a sulphocyanate is to 

 be recognized will be considered in connection with that liquid. In 

 the human subject, the parotid secretion is more abundant than that of 

 any other of the salivary glands ; but the entire quantity in the twenty- 

 four hours has not been directly estimated. 



In the horse, ass and ox, it has been found that when mastication is 

 performed on one side of the mouth, the flow from the gland on that 

 side is increased, exceeding by several times the quantity produced on 

 the opposite side. The flow of saliva from the parotid takes place with 

 increased activity during mastication. The opening of the parotid duct 

 is so situated that the liquid is discharged directly upon the food as it 

 is undergoing trituration by the teeth ; and as the secretion is more 

 abundant on the side on which mastication is going on and the con- 

 sistence of the liquid is such as to enable it to mix readily with the food, 



