DIGESTION. 289 



pulpy mass, and subsequently boiled in distilled water for about a quarter 

 of an hour. The glycogen is precipitated from the filtered decoction by 

 the addition of alcohol. Glycogen has been found in many other struc- 

 tures than the liver (See Appendix). 



Glycosuria. The facility with which the glycogen of the liver is 

 transformed into sugar would lead to the expectation that this chemical 

 change, under many circumstances, would occur to such an extent that 

 sugar would be present not only in the hepatic veins, but in the blood 

 generally. Such is frequently the case; the sugar when in excess in the 

 blood being secreted by the kidneys, and thus appearing in variable 

 quantities in the urine (G-lycosuria). 



Influence of the Nervous System. Glycosuria maybe experimentally 

 produced by puncture of the medulla oblongata in the region of the 

 vaso-motor centre. The better fed the animal the larger is the amount 

 of sugar found in the urine; whereas in the case of a starving animal no 

 sugar appears. It is, therefore, highly probable that the sugar comes 

 from the hepatic glycogen, since in the one case glycogen is in excess, 

 and in the other it is almost absent. The nature of the influence is 

 uncertain. It may be exercised in dilating the hepatic vessels, or pos- 

 sibly may be exerted on the liver cells themselves. The whole course 

 of the nervous stimulus cannot be traced to the liver, but at first it 

 passes from the lower part of the floor of the fourth ventricle and 

 medulla down the spinal cord as far as in rabbits the fourth dorsal 

 vertebra, and thence to the first thoracic ganglion. 



Many other circumstances will cause glycosuria. It has been ob- 

 served after the administration of various drugs, after the injection of 

 urari, poisoning with carbonic oxide gas, the inhalation of ether, chloro- 

 form, etc., the injection of oxygenated blood into the portal venous sys- 

 tem. It has been observed in man after injuries to the head, and in the 

 course of various diseases. 



The well-known disease, diabetes mellitus, in which a large quantity 

 of sugar is persistently secreted daily with the urine, has, doubtless, 

 some close relation to the normal glycogenic function of the liver; but 

 the nature of the relationship is at present quite unknown. 



THE INTESTINAL SECRETION, OR Succus ENTERICUS. 



On account of the difficulty in isolating the secretion of the glands 

 in the wall of the intestine (Brunner's and Lieberkiihn's) from other 

 secretions poured into the canal (gastric juice, bile, and pancreatic secre- 

 tion), but little is known regarding the composition of the former fluid 

 (intestinal juice, succus entericus). 



It is said to be a yellowish alkaline fluid with a specific gravity of 

 1011, and to contain about 2.5 per cent of solid matters (Thiry). 

 19 



