80 DISEASES OF THE HORSE. 



SACCHARINE IHABETES ( DIABETES MELLITUS, GLYCOSURIA, OR INOSURIa). 



This is primarily a disease of the nervous system or liver rather 

 than of the kidneys, yet, as the most j^rominent symptom is the sweet 

 urine, it ma}^ be treated here. 



Causes. — Its causes are varied, but resolve themselves largely into 

 disorder of the liver or disorder of the brain. One of the most 

 prominent functions of the liver is the formation of glycogen, a prin- 

 ciple allied to grape sugar, and passing into it by further oxidation in 

 the blood. This is a constant function of the liver, but in health the 

 resulting sugar is burned up in the circulation and does not appear in 

 the urine. On the contrary, when the supply of oxygen is defective, 

 as in certain diseases of the lungs, the Avhole of the sugar does not 

 undergo combustion and the excess is excreted by the kidneys. Also 

 in certain forms of enlarged liver the amount of sugar produced is 

 more than can be disposed of in the natural way, and it appears in the 

 urine. A temporary sweetness of the urine often occurs after a 

 hearty meal on starchy food, but this is due altogether to the super- 

 abundant supply of the sugar-forming food, lasts for a few hours 

 only, and has no pathological significance. In many cases of fatal 

 glycosuria the liver is found to be enlarged, or at least congested, and 

 it is found that the disorder can be produced experimentally by 

 agencies which produce an increased circulation through the liver. 

 Thus Bernard produced glycosuria by pricking the oblong medulla at 

 the base of the brain close to the roots of the pneumogastric nerve, 

 which happens to be also the nerve center (vaso-motor) which presides 

 over the contractions of the minute blood vessels. The pricking and 

 irritation of this center leads to congestion of the liver and the exces- 

 sive production of sugar. Irritation carried to this point through the 

 pneumogastric nerve causes saccharine urine, and. in keeping with 

 this, disease of the pancreas has been found in this malady. The com- 

 jilete removal of the pancreas, however, determines glycosuria, the 

 organ having in health an inhibitive action on sugar production by 

 the liver. The same result follows the reflection of irritation from 

 other sources, as from different ganglia (corpora striata, optic thalami, 

 pons, cerebellum, cerebrum) of the brain. Similarly it is induced by 

 interruption of the nervous control along the vaso-motor tracts, as in 

 destruction of the u])i)er or lower cervical sympathetic ganglion, by 

 cutting the nervous branch connecting these two, in injury to the 

 spinal marrow in the interval between the brain and the second or 

 fourth dorsal vertebra, or in disease of the celiac plexus, which 

 directly presides over the liver. Certain chemical poisons also cause 

 saccharine urine, notal)ly woorarn. strychnia, morphia, phosphoric 

 acid, alcohol, ether, quinia. chloroform, ammonia, arsenic, and 

 ])hlorizin. 



Symptoms. — The symptoms are ardent thirst and profuse secretion 



