684 PHYSIOLOGY. 



This organ of the nervous system is a secretory center for the 

 saliva. In the floor of the fourth ventricle at the level of the origin 

 of the facial nerve, and somewhat posterior to it, is found the 

 originating nucleus of the fibers of the intermediary nerve of Wris- 

 berg. This, through the chorda tympani of the facial nerve, is car- 

 ried to the submaxillary gland. Pricking the center or stimulating 

 it electrically provokes a copious secretion of saliva. Certain patho- 

 logical lesions may produce the same thing. 



GLUCOSE SECRETION. The puncture in the fourth ventricle 

 should be limited superiorly by a line joining the origin of the audi- 

 tory nerves, and inferiorly by one joining the origins of the vagi. 

 This will determine within an hour the condition known as diabetes 

 mellitus glucose in the urine. 



The diabetes ceases if the liver be extirpated, and is not pro- 

 duced if the liver has been previously taken away, .or its vessels have 

 been previously tied. In the liver of animals rendered diabetic in 

 such a manner there is found an intense vasomotor paralysis. 



The present theory is that the diabetic puncture produces sugar 

 in the blood by irritation of the glyco-secretory centers in the medulla, 

 which send fibers down the cervico-dorsal cord to the solar plexus and 

 then in the trunk of the splanchnics to the liver-cell. It has been 

 shown by E. Cavazzini that irritation of these nerves produces his- 

 tological changes in the hepatic cells. Ligature of the aorta and portal 

 vein, thus arresting the circulation, does not prevent these changes in 

 the liver-cell. Irritation of the central and peripheral ends of the 

 vagus increases the sugar in the blood. Section of the vagi causes 

 the glycogen to leave the liver and tissues and the sugar to be absent 

 in the blood. 



The action of the medulla upon the liver is exercised by means 

 of the spinal cord through the intervention of the great sympathetic. 



The oblongata centers are: (1) respiratory, (2) vasoconstrictor 

 and vasodilator, (3) cardio-inliibitory , (4) cardio-accelerator, (5) 

 diabetic center, (6) vomiting center, (7) deglutition, (8) salivation, 

 (9) mastication, and (10) cilio-spinal. 



ANATOMY OF THE CEREBELLUM. 



The cerebellum is situated at the posterior and inferior portion 

 of the brain. 



The cerebellum is entirely covered by the occipital lobes of the 

 cerebrum in man, but only incompletely so in monkeys. It is united 

 by the cerebellar peduncles to the cerebrum, pons, and medulla. 



