ORGANS OF ABSORPTION. 273 



cially, has shown that, if all the sympathetic nerves leading 

 to the liver of a frog be tied, diabetes can no longer be pro- 

 duced, either by puncture of the fourth ventricle or by elec- 

 trical excitation of the spinal cori. In all these cases violent 

 hyperaemia of the liver appears to be necessary to the excite- 

 ment of its glycogenic functions; indeed, if the inferior 

 vena cava below the liver in a frog be tied, an increase 

 of circulation in the portal vein is produced, followed by 

 diabetes. This increase of circulation is caused by the 

 anastomoses existing in this animal, between the venous sys- 

 tem in general and the system of the portal vein. The con- 

 gestion of the liver and excitation of its glycogenic function 

 which follow a puncture made in the fourth ventricle do not, 

 however, appear to be produced simply by a (nervous) para- 

 lytic hyperaBmia, arising from the abolition of the vaso- 

 motor innervation; because the artificial diabetes thus 

 produced is but temporary (lasting, at the most, twenty-four 

 hours). This diabetes appears rather to arise from the excita- 

 tion of certain nerves included in the network of the great 

 sympathetic nerve, and which are to the liver what the 

 chorda tympani is to the sub-maxillary gland (Cl. Bernard). 



D. Organs of absorption. Function of the chyliferous 

 vessels. 



We have seen how the digested matters reach the very 

 substance of the villus by means of the epithelium. While 

 the epithelium is being renewed (desquamation, etc.), the 

 body of the villus empties its contents, and the absorbed 

 elements are diffused into or through the vessels. 



These vessels, however, are of two kinds : we have seen 

 that there is a vascular blood network, forming the origin of 

 the portal vein, and a central chyliferous vessel, the origin 

 of the chyliferous vessels, which open into the principal trunk 

 of the lymphatic circulation (thoracic duct. See lymphatic 

 si/stem, p. 156). The blood current, being placed so near 

 the surface, is evidently in the most favorable situation to 

 absorb whatever is brought to it by the epithelium: it is, 

 therefore, generally supposed that the greater part of the 

 absorbed matters are carried along by the blood ; and it is 

 true that we find the peptones and glucose again in the 

 portal vein. But, while the fat is disappearing from the villus, 

 we find that the central chyliferous vessel becomes quite white, 

 and that a large number of delicately emulsionized fat mole- 

 cules make their appearance in it ; this seems to show that 



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