342 THE ADRENAL, GENERAL MOTOR, AND VAGAL SYSTEMS. 



starting from an ulcerated area and directed toward an hepatic 

 focus has also been observed. When the primary portal struct- 

 ures are normal, transmission of the putrid material may occur 

 through the lymphatics. While this fact seems admissible, it 

 has not been verified." Again, pathological conditions of the 

 stomach, pancreas, or spleen may supply the portal vein with 

 pathogenic elements. In the normal subject, however, the 

 liver-tissues per se are totally isolated anatomically from any of 

 the structures that come into contact with exogenous bacteria, pre- 

 cisely as they are in other organs: the muscles, the heart, etc. 

 That its blood-stream affords protection from disease is un- 

 doubted, however, judging from the leucocytes that are con- 

 stantly entering the organ, and the perivascular lymphatic 

 channels. That the portal vein is also an important field for 

 the splitting of toxalbumins and their reduction to harmless 

 bodies we shall also see. But it seems quite clear that the liver 

 itself is not primarily a germ-killing organ, and that its at- 

 tributes are essentially chemical. This removes the hepatic 

 cell still further from the functions now attributed to it, and 

 suggests that the oxidizing substance in the lobular blood- 

 vessels may be the main source of the liver's functional activity. 



This brings us to the consideration of the functions in 

 which the oxidizing substance in the blood-plasma acts as a 

 reagent. We have already reviewed, in this connection, the 

 synthesis of haemoglobin; we will now take up and consider 

 two equally important subjects: i.e., the origin of urea and the 

 conversion of sugar into glycogen. 



Urea and its Formation. We will first analyze an experi- 

 ment by Schroder 20 in which the liver was taken from a freshly- 

 killed dog and irrigated through its blood-vessels by a supply 

 of blood taken from another animal. Howell refers to this 

 experiment in the following words: "If the supply of blood 

 was taken from a fasting animal, then circulating it through 

 the isolated liver was not accompanied by any increase in the 

 amount of urea contained in it. If, on the contrary, the blood 

 was obtained from a well-fed dog, the amount of urea con- 



20 Schroder: Archiv fur exper. Pathol. und Pharm., Bd. xv aad xix, 1882 and 

 1885. 



