196 



OF ABSORPTION AND SANGUIFICATION. 



smaller diameter than the portion of intestine, c, as in the figure, the fluid 

 will discharge itself with difficulty, the intestine will become tight, and an 

 effusion of the colored fluid into the pure water contained in the vessel, A, 

 will become apparent; but if the diameter of the siphon be greater than that 



FIG. 82. 



of the intestine attached to it, the discharge of the fluid will take place 

 easily, the membranous tube will become flaccid, and a rapid process of ab- 

 sorption of the water or of any saline solution in A will occur. 1 In a recent 

 paper by Professor Graham, 2 of great interest in reference to the phenomena 

 we are now discussing, that chemist shows that some substances, as the salts 

 of the metals, generally pass through porous septa with facility; and these 

 and all substances so diffusing themselves he proposes to call crystalloids; 

 whilst others, as alumina, hydrated silicic acid, gum dextrin, gelatin, albu- 

 minous substances, etc., pass with great difficulty, or not at all. These he 

 denominates colloids. 3 The latter are characterized by possessing feeble 

 chemical reactions; by diffusing very slowly in water; by having so weak an 

 affinity for that liquid that they are easily precipitated from their solution; 

 by being unable to pass through (by means of diffusion) any colloidal sep- 

 tum ; by their consequent insipid taste, since they probably never reach the 

 sentient extremities of the gustatory nerves; and by their high equivalent 

 numbers, unstable nature, and ready passage into decomposition. The crys- 

 talloids, on the other hand, present characters which are precisely the 

 reverse. 



[While it is true that colloids are of low diffusibility in their natural con- 

 dition, they may, however, be caused to undergo certain chemical or physi- 

 cal changes, in consequence of which they become capable of osmosis, and 

 thus become practically crystalloids. As examples of this metamorphosis, 

 may be mentioned the conversion of the colloid albumen into the crystalloid 

 albuminose in the process of gastric or intestinal digestion, and the change 

 which occurs in oily matters by contact with the pancreatic juice, whereby 

 an emulsion is formed aud absorption rendered possible. These changes, 

 however, are alluded to at considerable length in the text. 



Crystalloids not only diffuse among themselves, but they will gradually 



1 Robinson, Contributions to Physiology, 1857, p. 98. 



Trims. Royal Soc., 1SU1, part i. 



' lied wood, Dialysis, Phann. Journ., April, 1802. 



