MOTION OF THE JUICES OF THE ANIMAL BODY. 



thoroughly dried, and the tube filled with mercury and inverted, so that the open, 

 narrow end stands in a cup of mercury, the mercury in the tube falls to about 27 

 inches (Hessian,) and remains, if the bladder have no flow, at that height, rising and 

 falling as the mercury does in a barometer. 



No air passes through the dry bladder into the Torricellian vacuum thus pro- 

 duced. When, by proper manipulation, we have allowed to pass out as much as 

 can be removed of the air still contained in the tube, we have, in this arrangement, 

 a barometer, containing no more air than would be found in one made with a 

 similar tube hermetically sealed at the wide end, provided the mercury in the 

 latter had not been boiled in the tube to expel the last traces of air. By the 

 desiccation of the bladder, its pores, which allowed a passage to water, brine, oil, 

 or even mercury, have obviously been closed by the adhesion of the successive 

 layers of membrane, which perhaps cross each other, so that the bladder is not 

 more permeable for the particles of air than a slice of horn of the same thickness. 



p> 



If we introduce water into the tube in the posi- 

 tion, Fig. 10, to the line marked 6, and, after fill- Fig. 11. 

 ing the narrow part of the tube with mercury, 

 invert it in a vessel of mercury, Fig. 11, we 

 observe a number of minute bubbles of air passing 

 through the moist bladder into the tube. The 

 mercury falls to a certain point, which is higher 

 or lower according to the thickness of the bladder; 

 it stands at a lower level with a thin membrane 

 than with a thick one. When a single layer of 

 ox-bladder is used, it falls to 12 inches (above 

 the level of the mercury in the vessel ;) with a 

 double layer it stands at from 22 to 24 inches. 



If we take care to allow the water standing 

 above the mercury to enter the wide part of the 

 tube, so that the bladder is kept at all times 

 covered with water, the mercury remains stationary 

 at the same level. If, for example, it stood at 

 12 inches, it remains there, although the quantity 

 of water is constantly diminishing by evaporation 

 from the bladder ; and it maintains its level, even 

 after all the water has disappeared. 



The height of the mercury in the narrow tube is an exact measure of the pres- 

 sure acting on the surface of the bladder. The pressure in the inside of the tube 

 is less than the existing pressure of the atmosphere outside by the height of that 

 column of mercury. 



This difference of level between the mercury in the vessel and that in the tube 

 is the limit of the pressure, under which air passes into the water through the 

 pores of the bladder ; or under which the molecules of water in the pores are 

 displaced by the molecules of air. 



If we fill the tube entirely with water, and place the narrow end in mercury, 

 while the wide end, closed with bladder, is exposed to the air, the mercury rises 

 in the narrow limb, and at last reaches a point, identical with that to which it fell 

 in the preceding experiment. For each specimen of bladder, according to its 

 thickness, the level to which the mercury reaches is of course different. 



When the diameter of the wide part of the tube, which is closed with bladder, 

 is 12 millimetres, and that of the narrow tube 1 millimetre, the mercury rises, 

 with ox-bladder, according to the temperature and the hygrometric condition of the 

 air, to from 22 to 65 millimetres in one hour. 



The cause of the rise of the mercury in this experiment hardly requires a special 

 explanation. 



The bladder is penetrated with water, covered on one side with water, and on 

 the other in contact with a space (the air) not saturated with aqueous vapour 

 The water contained in the pores of the side of the bladder turned towards the air 



