HUMAN PHYSIOLOGY. 



alkaline medium. The change consists in the assumption of a molecule 

 of water. 



Starch. Water. Grape Sugar. 



C 6 H 10 5 + H 2 = C 6 H 12 6 



NERVOUS CIRCLE OF INSALIVATION. 



AFFERENT OR EXCITOR NERVES. EFFERENT OR MOTOR NERVES. 



1. Lingual branch of 5th pair. I. Auriculo-temporal branch of 5th 



2. Glosso-pharyngeal. pair, for parotid gland. 



2. Chorda tympani, for sub-maxil- 

 lary and sub lingual glands. 



The centres regulating the secretion are two, viz. : The medulla oblon- 

 gata and the submaxillary ganglion of the sympathetic ; the latter acting 

 antagonistically to the former. Impressions excited by the food in the 

 mouth reach the medulla oblongata through the afferent nerves ; motor im- 

 pulses are there generated which pass outward through the efferent nerves. 



Stimulation of the auriculo-temporal branch increases the flow of saliva 

 from the parotid gland ; division arrests it. 



Stimulation of the chorda tympani is followed by a dilation of the blood 

 vessels of the sub-maxillary gland, increased flow of blood (thus acting as 

 a vaso-dilator nerve) and an abundant discharge of a thin saliva ; division 

 of the nerve arrests the secretion. 



Stimulation of the cervical sympathetic is followed by a contraction of 

 the blood vessels, diminishing the flow of blood (thus acting as a vase-con- 

 strictor nerve) and a diminution of the secretion, which now becomes thick 

 and viscid ; division of the sympathetic does not, however, completely 

 dilate the vessels. There is evidence of the existence of a local vaso- 

 motor mechanism, which is inhibited by the chorda tympani ; exalted by 

 the sympathetic. 



Deglutition is the act of transferring food from the mouth into the 

 stomach, and may be divided into three stages : 



1. The passage of the bolus from the mouth into the pharynx. 



2. From the pharynx into the oesophagus. 



3. From the oesophagus into the stomach. 



In the ist stage, which is entirely voluntary, the mouth is closed and 

 respiration momentarily suspended; the tongue, placed against the roof 

 of the mouth, arches upward and backward, and forces the bolus into the 

 fauces. 



In the 2d stage, which is entirely reflex, the palate is made tense and 

 directed upward and backward by the levatores-palati and tensores-palati 



