iQii] William J. Gies 297 



(poor in oxygen and rieh in CO2). This high carbon dioxide content 

 of the blood returning from the intestinal tract increases the affinity of 

 the colloids of the blood for water in consequence of which they absorb 

 it through the intestinal mucosa from the lumen of the intestine as 

 long as it is present there. The experiments of von Limbeck, Gürber, 

 and Hamburger^^ show that under the influence of such an increase in 

 CO2 concentration as exists normally in venous blood over arterial 

 blood the red and white corpuscles absorb an amount of water which 

 easily amounts to from 5 to over 15 per cent.^* of their volume in 

 arterial blood. If we use only the lower of these values and ignore 

 entirely the water carrying power of the colloids contained in the 

 plasma, a little calculation shows that a liter of blood passing through 

 the intestinal tract is capable of absorbing 17.5 c.c. of water, for the 

 corpuscles when moist make up in round numbers about 35 per cent. 

 of the blood. Even these values, which have been chosen as low as pos- 

 sible, easily suffice to account for the absorption of great amounts of 

 water from the gastro-intestinal tract. (Page 186.) 



It requires no special explanation when we say that the reverse of 

 all these conditions hold when the kidneys are reached. In its transit 

 through the lungs the venous blood loses the carbon dioxide responsible 

 for the increased affinity of its colloids for water. When, now, the 

 arterial blood reaches the kidneys — which, let it be noted, are supplied 

 with extra large arteries — more water is contained in the blood than 

 the blood colloids are capable of holding, and so this separates off as 

 urine.^^ These considerations show why a water absorption is the rule 

 in the intestine and a water secretion the rule in the kidney. How under 

 the influence of an acid the absorption of water by any colloid is 



'* Hamburger, Osmotischer Druck und lonenlehre, Wiesbaden, 1902, i, p. 291 ; 

 ibid., p. 404. 



"These figures are nearly doubled if instead of comparing the sizes of the 

 corpuscles in arterial and in ordinary venous blood the sizes in arterial and pas- 

 sively congested venous blood are compared. In other words, the same circum- 

 stances that make the passively congested organ become edematous make the 

 corpuscles in the blood become " edematous." 



"The question that naturally arises is why the secretion of water does not 

 occur into the lungs (where the CO2 escapes) instead of through the kidneys. 

 The reason may be twofold. The colloidal membrane between blood and alveo- 

 lus may not be freely permeable to water (just as the urinary membrane is not 

 in acute parenchymatous nephritis) or the time necessary for a reversal of the 

 water absorption may be greater than the time the blood spends in traversing 

 the lung capillaries. 



