280 ABSORPTION AND SANGUIFICATION. 



in many of the lower animals, they are spread out into broader laminae 

 at the base, and are connected together so as to form ridges or folds. 



493. The nutritive materials taken up by the blood-vessels of the ali- 

 mentary canal, are not conveyed directly into the general circulation ; 

 for they are first submitted to the -agency of the Liver. All the veins 

 which return the blood from the gastro-intestinal capillaries, converge 

 into the portal trunk, which distributes it to the various portions of that 

 secreting apparatus ;. and there is strong reason to believe, that not 

 merely is the fluid there depurated of some matters whose presence 

 would be injurious, but that the Liver exercises a powerful assimilating 

 action upon the proper nutritive substances, rendering them fitter to 

 become components of the Blood. For the blood of the portal vein, 

 when examined during digestion, is found to contain a large proportion 

 of albumen and comparatively little fibrine ; whilst in that which has 

 passed through the liver, the amount of fibrine has undergone a large 

 increase. Again, it appears that fatty matters are elaborated in the 

 liver, either from saccharine substances, or from albuminous compounds ; 

 for even when no fat can be detected in the blood of 'the vena portse, 

 that of the hepatic vein contains it in considerable amount. So, again, 

 it appears that the liver elaborates from some other constituents of the 

 blood a saccharine compound (diabetic sugar), which is destined for im- 

 mediate elimination by the lungs, and which, being much more readily 

 carried off by the respiratory process than either grape-sugar or cane- 

 sugar, may be regarded as its most appropriate pabulum. Further, if 

 white of egg mixed with water be injected into any of the systemic veins, 

 distinct evidence of the presence of albumen is speedily traceable in the 

 urine ; showing that this substance has not been properly assimilated. 

 But if the same fluid be injected into the portal system, no trace of its 

 presence in the urine is found. So, again, when a solution of sugar is 

 injected into the general venous system, this substance soon shows itself 

 in the urinary excretion ; but if the same injection be made into the 

 vena portse, so that the sugar is obliged to pass through the liver, no 

 such elimination takes place, it being then assimilated with the blood. 

 The liver, however, is not required to effect a corresponding change in 

 the fatty matters taken up from the food ; for these are received into 

 the blood through the absorbents, rather than through the sanguiferous 

 vessels; and it is found that if fatty matters be injected into the general 

 circulation, no effect is produced on the urine.* 



494. Every one of the intestinal Villi, however, also contains the 

 commencement of a proper lacteal vessel ; the portion of the absorbent 

 system specially adapted for the reception of alimentary matters from 

 without, being thus distinguished, on account of the milky aspect of the 

 fluid which is found within it. The following figure (83) represents the 

 appearance offered by the incipient lacteals, in a villus of the jejunum 

 of a young man, who had been hung soon after taking a full meal of 

 farinaceous food. The trunk that issues from the villus is formed by 

 the confluence of several smaller branches, whose origin it is difficult to 

 trace ; but it is probable that they form loops by anastomosis with each 



* See the recent Lectures and Memoirs of M. Cl. Bernard, in " L'Union Medicale," 

 and the "Gazette Medicale," for 1850. 



