148 J. F. MCCLEXDOX. 



be slightly more permeable to some one ion than to others. If 

 this ion were more concentrated in the plasma or in the corpuscle, 

 the latter would become electrically charged, and a general in- 

 crease in ionic permeability would lead to a reduction or loss 

 of this charge. The loss of charge would favor their coming 

 in contact with one another and their precipitation, but their 

 cohesion is probably due to some other change, possibly the exit 

 of adhesive substances, on increase in permeability. 



VI. ABSORPTION AND SECRETION. 

 i. Absorption through the Gut. 



If a live vertebrate intestine be filled with one portion of a 

 physiological NaCl solution, and suspended in another portion 

 of the same solution, fluid will pass through the wall of the gut 

 from within outward. Cohnheim 1 found that holothurian gut 

 behaves in the same way toward sea water, and the absorption 

 stops if the gut is injured with chloroform or sodium fluoride. 



It might be supposed that the hydrostatic pressure produced 

 by the contraction of the musculature, is the driving force of 

 absorption, but on the contrary, Reid 2 found that the wall of 

 the rabbit's intestine behaved in the same way when used as a 

 diaphragm. 



Salt is absorbed by an intestine filled with a very hypotonic 

 solution of it, and water may be absorbed when the solution is 

 very hypertonic. 



Blood salts enter the intestine when it is injured by an ex- 

 tremely hypertonic solution, or sodium fluoride, chinin or arsenic. 



Grape sugar and sodium iodide may pass from without inwards 

 through the wall of a normal holothurian intestine. 



Traube 3 claims that absorption is explained by his observation 

 that the surface tension of the contents of the gut is less than 

 that of the blood, but this does not apply to the experiments in 

 which an identical solution was placed on each surface of the 

 wall of the gut. Traube 4 found that the addition of a substance 



1 Zeil. physiol. Chem., 1901, XXXIII., 9. 

 '-Jour. Physiol., 1901, XXVI.. 436. 



3 Pfliiger's Arch., 1904, CV., 559. Cf. Iscovesco, Comptes Rendus, Soc. I 

 1911, I. XXI., 637. 



4 Biochem. Zeit., 1910, XXIV., 323. 



