374 USES OF THE LIVER DUCTLESS GLANDS 



during life by a catheter introduced into the right cavities of the heart ; 

 while in the carnivora, under a purely animal diet, no sugar is contained 

 in the blood of the portal system. The normal blood contains, perhaps, 

 a small quantity of sugar 0.5 to I part per thousand but the pro- 

 portion is always greater in the blood of the hepatic veins. 



The characters of animal sugar do not materially differ from those 

 of glucose, except that it ferments more readily and is destroyed in the 

 system with great facility. This property of the sugar resulting from 

 the glycogen formed in the liver probably is of great importance. The 

 sugar which results from digestion is all carried to the liver. Here it is 

 changed into glycogen ; and it is probable that without this change into 

 glycogen and its subsequent transformation into what is called liver- 

 sugar, it is not perfectly adapted to the purposes of nutrition. 



The sugar discharged into the venous system by the hepatic veins 

 usually is lost in the passage of the blood through the lungs. The ques- 

 tion of the final destination of sugar will be taken up again in connec- 

 tion with the physiology of nutrition. 



Conditions that influence the Quantity of Sugar in the Blood. It is 

 probable that disturbances of the circulation in the liver are the most 

 important conditions influencing the discharge of sugar by the hepatic 

 veins, and these operate mainly through the nervous system. 



A notable experiment on the influence of the nervous system on the 

 liver is the one in which artificial diabetes is produced by stimulation of 

 the floor of the fourth ventricle (Bernard). This operation is not dif- 

 ficult. The instrument used is a delicate stilet, with a flat cutting ex- 

 tremity and a small projecting point about 2 V f an m h millimeter) 

 long. In performing the operation on a rabbit, the head of the animal 

 Is firmly held in the left hand, and the skull is penetrated in the median 

 line, just behind the superior occipital protuberance. This can easily be 

 done by a few lateral movements of the instrument. Once within the 

 cranium, the instrument is passed obliquely downward and forward, so 

 as to cross an imaginary line drawn between the two auditory canals, 

 until its point reaches the basilar process of the occipital bone. The 

 point then penetrates the medulla oblongata, between the roots of the 

 auditory nerves and the pneumogastrics, and its projection serves to 

 protect the nervous centre from more serious injury from the cutting 

 edge. The instrument is th'en carefully withdrawn and the operation is 

 completed. This experiment is almost painless, and it is not desirable 

 to administer an anesthetic, as this, in itself, would disturb the glyco- 

 genic process. The urine may be obtained before the operation, by press- 

 ing the lower part of the abdomen, taking care not to allow the bladder 

 to pass up above the point of pressure, and it will be found turbid, alka- 



