14 MOTION OF THE JUICES OF THE ANIMAL BODY. 



If we lay together, one over the other, two portions of bladder, saturated with 

 solution of salt of sp. g. 1-204, and over the upper one another piece of bladder of 

 equal size, saturated with water, and if we allow them to remain thus, without 

 pressure, we find, after some minutes, when the two pieces saturated with solution 

 of salt are separated, that drops of saline solution appear between them, of which 

 no trace could previously be perceived. If the piece of bladder saturated with water 

 contained 5 volumes of water, and the next piece 3 volumes of saline solufion, 

 there must be produced, by the mixture of both, 8 volumes of diluted saline solufion, 

 of which each piece of bladder must contain one half, or 4 volumes, if the absorbent 

 power of the portion saturated with the original saline solution were increased by 

 the addition of water in the same ratio as the absorbent power of the portion satu- 

 rated with water was diminished by the addition of salt. The saline liquid would 

 have given up 1^ volume of saline solution to the other, and would have received 

 from it 2 volumes of water. In this case, the mixture in the two upper pieces 

 of bladder would occupy the same space which its constituents, water and saline 

 solution, occupied in each singly. But the efflux of the liquid towards the third or 

 lowest piece of bladder saturated with saline solution, proves, that the two uj>per 

 pieces retain a smaller volume of the mixture newly formed in their pores, than the 

 one piece absorbed of water alone, and the other of saline solution alone. The 

 power of retaining water is diminished by the addition of salt to the bladder 

 saturated with water ; liquid is expelled ; but by the addition of this water to the 

 bladder moistened with saline solution, the absorbent power of this piece of blad- 

 der is increased, not in the same ratio according to which the proportion of salt is 

 diminished, but in a less ratio. 



The experiments above described show that the attraction of the porous sub- 

 stances for the water which they have absorbed does not prevent the mixture of this 

 water with other liquids. 



The permeability of animal tissues to liquids of every kind, and the miscibility 

 of the absorbed liquids with others which are brought in contact with the tissues, 

 may be demonstrated by the simplest experiments.* 



If we moisten one side of a thin membrane with ferrocyanide, of potassium, and 

 the opposite side with chloride of iron in solution, we perceive in the substance of 

 the membrane a spot of Prussian blue immediately deposited. (JoH. MTLLER.) 



All fluids which, when brought together, suffer a change in their nature cr in 

 their properties, exhibit, when only separated by an animal membrane, exactly 

 analogous results ; they mix in the pores of the membrane, and the decomposition 

 commences in its substance. 



If we tie up one end of a cylindrical glass tube with bladder, and fill it to the 

 height of 3 or 4 inches with water or strong brine, neither the water nor the brine 

 flows out through the pores of the bladder/under this slight pressure. 



But if we leave the tube containing brine exposed to evaporation in the air, the 

 side of the bladder exposed to the air is soon covered with crystals of salt, which 

 gradually increase, so as to form a thick crust.t It is obvious that the pores of the 

 bladder become fluid with brine ; that, on the side exposed to the air, the water 

 evaporates ; its place is supplied by fresh brine, and the dissolved salt is deposited 

 at the external minute openings of the pores, in the form of crystals. If the tube 

 be filled originally with dilute saline solution, the crust of salt is not formed on the 

 outer surface of the bladder until the solution in the tube has reached, by evapora- 

 tion, the maximum of saturation. Before this takes place, we can perceive in the tube, 

 if we set the liquid in motion, two strata, a heavier and a lighter, the latter swim- 

 ming on the former. When these strata can no longer be observed, the liquid is 

 in every part saturated with salt; and now, by further evaporation, crystals are 

 deposited on the outer surface of the bladder. This last circumstance proves that 

 the amount of salt in the liquid is uniformly distributed from below upwards, from 

 the specifically heavier to the specifically lighter part. 



If we immerse the tube closed with bladder, and filled with saline solution, in 

 pure water, the latter acquires the property of precipitating nitrate of s'lver, even 



* Animal tissues are permeable to liquids of every kind, which act on each othe: in the sub- 

 taace of the tissues, 

 t Deposition of salt on the outside of bladder from brine on the inside. 



