ABSORPTION. 217 



blood-vessels and carried direct to the liver. Analysis of the blood of the 

 portal vein after the ingestion of large quantities of sugar may reveal an 

 increase to 0.25 per cent.; while after the injection of sugar into the intestine 

 the percentage may rise as high as 0.4 per cent. As chemic analysis of 

 lymph obtained from the thoracic duct shows no increase in the percentage 

 of sugar beyond that normally present (o.i per cent.), it is assumed that 

 sugar is not removed from the villi by the lymph-vessels. 



On reaching the liver a portion of the sugar 12 to 20 per cent, passes from 

 the blood stream through the walls of the capillaries into surrounding lymph 

 spaces and comes into direct relation with the liver cells. Then through the 

 agency of an enzyme, the sugar is dehydrated, converted into starch and 

 stored for a variable length of time in the liver cells in the form of minute 

 granules which can be readily seen with the aid of the microscope. Under 

 this form the carbohydrate material is retained until the necessity arises 

 for its return to the blood, and this happens, when the percentage of sugar in 

 the blood falls below the normal, viz., 0.05 to 0.15 per cent. Under such 

 circumstances the necessary amount of the liver starch is hydrated, con- 

 verted into sugar, and passed into the blood in quantities sufficient to restore 

 the normal percentage. The apparent necessity for this temporary storage 

 of sugar in the liver is to prevent its too rapid entrance into the arterial 

 blood and hence a rise in the percentage far beyond that which is normal. 

 Should this occur a condition known as hyperglycemia would result and 

 as a consequence an elimination of the excess by the kidneys giving rise to 

 the condition known as glycosuria. 



Absorption of the Products o) Protein Digestion. For the reason 

 that the proteins are for the most part transformed through hydra tion and 

 cleavage by the action of the gastric and pancreatic enzymes into peptones 

 and for the further reason that the peptones are diffusible bodies, it was 

 formerly believed that they represented the final stages in the digestion of 

 the proteins, and as such were absorbed out of the intestinal contents by 

 the action of the epithelium covering the villi. Though the production of pep- 

 tones was believed to be a necessary process before the absorption of protein 

 material could be effected, yet it was apparently demonstrated by the results 

 of experimentation that unchanged native protein, e.g., egg- albumin and 

 partially digested proteins, e.g., proteoses, were also absorbed though in 

 far less amounts. It has also been demonstrated that native proteins can 

 be absorbed by the mucous membrane of the large intestine. Inasmuch 

 as chemic analysis has failed to detect more than a trace of either peptone or 

 native protein in the portal blood or in the lymph of the thoracic duct, it 

 must be assumed that the epithelium after absorbing must also synthesize 

 them into some form of coagulable protein (plasma-albumin) which is 

 readily assimilable by the blood. That such a reconversion is necessary 

 would appear from the fact that the introduction of peptones even in small 

 amounts into the blood is followed by their elimination unchanged in the 

 urine. When injected into the blood in large amounts, they act as toxic 

 agents, giving rise to a fall of blood-pressure, a diminished coagulability of 

 the blood, coma, and death. 



After passing through the epithelium into the spaces of the villi the recon- 

 structed or synthesized plasma-protein molecules are removed by the blood- 



