120 



HUMAN PHYSIOLOGY. 



classes of food principles albumins, sugars, starches, and fats 

 there are formed peptones, glucose, and 'fatty emulsion, which differ 

 from the former in being highly diffusible a condition essential to 

 their absorption. In order that these substances may get into the 

 blood, they must pass through the layer of cylindric epithelial cells 

 and the underlying basement membrane, and into the lymph-spaces 

 of the villi and submucous tissue. The mechanism by which the cells 

 effect this passage of the food is but imperfectly understood. Os- 

 mosis and filtration are conditions, however, made use of by the 

 cells in the absorptive process. 



The products of digestion find their way into the general circula- 

 tion by two routes : 



1. The water, peptones, glucose, and soluble salts, after passing into 

 the lymph-spaces of the villi, pass through the wall of the capillary 

 blood-vessel ; entering the blood, they are carried to the liver 

 by the vessels uniting to form the portal vein ; emerging from the 

 liver, they are emptied into the inferior vena cava by the hepatic 

 vein. 



2. The emulsified fat enters the lymph-capillary in the interior of 

 the villus ; by the contraction of the layer of muscle-fibers sur- 

 rounding it its contents are forced onward into the lymph-vessels 

 or lacteals, thence into the thoracic duct, and finally into the blood 

 stream at the junction of the internal jugular and subclavian 

 veins on the left side. 



Properties and Composition of Lymph. Lymph, as found in the 

 lymph-vessels of animals, is a clear, colorless, or opalescent fluid, 

 having an alkaline reaction, a saline taste, and a specific gravity of 

 about 1040. It holds in suspension a number of corpuscles resem- 



COMPOSITION OF LYMPH. 



Water 95-536 



Proteids (serum-albumin, fibrin-globulin) . . . 1.320 



Extractives (urea, sugar, cholesterin) . . . . 1-559 



Fatty matters a trace 



Salts 0.585 



bling in their general appearance the white corpuscles of the blood. 

 Their number has been estimated at 8,200 per cubic millimeter, 



