INFLUENCE OF THE MEMBRANES ON THE SECRETIONS. 31 



through the urinary passages. If we add to the water colored or odorous matters, 

 these appear, more or less changed in the urine. When a small quantity of 

 ferrocyanide of potassium is added, its presence in the urine is very soon detected 

 by chloride of iron, which forms with it Prussian blue. Of concentrated solutions 

 far less is absorbed in the same time, than of diluted; in most cases they mix with 

 solid matters collected in the rectum, and are expelled in the form of a watery 

 dejection. 



All salts do not act alike in this respect. In equal doses, the purgative action of 

 Glauber salt and Epsom salt is far stronger than that of sea salt; and their power 

 of being absorbed by animal membranes appears to be in the inverse ratio of this 

 effect. It is hardly necessary, particularly to point out that an explanation of the 

 action of purgatives in general cannot be included in the above-described action of 

 saline solutions on the organism. The example which has been given is intended 

 to illustrate a physical property common to a large number of salts, and apparently 

 of the nature of the acid or base of the salt ; for chloride of calcium, chloride of 

 magnesium, bitartrate of potash, tartrate of potash and soda, phosphate of soda, and 

 certain doses of tartar emetic, show the same action as sea salt, Glauber salt, and 

 Epsom salt, although the bases and acids in these different salts are not the same. 



Solutions of cane sugar, grape sugar, sugar of milk, and gum, exhibit, when 

 separated from water by an animal membrane, phenomena similar to those exhibited 

 by the above-named solutions of mineral salts, without causing in the living body a 

 purgative action, when of equal concentration. The cause of this difference 

 may be that the mineral salts, in their passage through the intestinal canal, and 

 through the blood, are not essentially altered in their composition, while these 

 organic substances, in contact with the parietes of the stomach, and under the 

 influence of the gastric juice, suffer a very rapid change, by which the action which 

 they have out of the body is arrested. 



Since the chemical nature and the mechanical character of mebranes and skins 

 exert the greatest influence on the distribution of the fluids in the animal body, 

 the relations of each membrane presenting any peculiarity of structure, or of the 

 different glands and systems of vessels, deserve to be investigated by careful 

 experiment ;* and it might very likely be found that in the secretion of the milk, 

 the bile, the urine, the sweat, &c., the membranes and cell-walls play a far more 

 important part than we are inclined to ascribe to them ; that besides their physical 

 properties, they possess certain chemical properties, by which they are enabled to 

 produce decompositions and combinations, true analyses ; and if this were ascer- 

 tained, the influence of chemical agents, of remedies, and of poisons on those 

 properties, would be at once explained. 



The phenomena described in the preceding pages are observed, not in the 

 gelatinous tissues alone, but also, apparently, in many other structures of the animal 

 body, which cannot be reckoned as belonging to that class.t 



If we tie moist paper over the open end of a cylindrical tube, and, after pouring 

 in above the paper white of egg to the height of a few lines, place that end of 

 the tube in boiling water, the albumen is coagulated, and when the paper is removed, 

 we have a tube closed with an accurately fitting plug of coagulated albumen, 

 which allows neither water nor brine to run through.;}; If the tube be now filled 

 to one-half with brine, and immersed in pure water, as in Fig. 4, the brine is seen 

 gradually to rise ; and in three or four days it increases by from | to of its 

 volume, exactly as if the tube had been closed with a very thick membrane 



Influence of the cutaneous evaporation on the motion of the fluids of the 



animal body. 



When a tube about 30 inches long, bent in the form of a knee, and widened at 

 one end, is tied over at that end with a piece of moist ox-bladder, the bladder now 



* Influence of membranes on secretions. 



t These phenomena not confined to the gelatinous tissues. 



t Coagulated albumen acts like a thick membrane. 



