50 



HISTORY OF THE VEGETAT3LE KINGDOM. 



the syrup passes outwards into tlie water, and is 

 indicated by its imparting a sweetish taste to 

 the fluid. Or if a solution of common salt be 

 substituted, and submitted to the same process, 

 the escape of the saline solution will be immedi- 

 ately proved by the water becoming white on 

 the addition of a few drops of solution of nitrate 

 of silver. The transmission of fluids, then, is 

 always reciprocal, but that power predominates 

 which transfers the lighter to the denser fluid. 

 Similar experiments were performed with the 

 swimming bladder of the carp, and also with 

 the pods of the bladder senna, and the same 

 results occurred, yet all pervious substances do 

 not possess the same properties. Having ob- 

 served this state of distension, which was acquired 

 by membranous bags through the influence of 

 endosmose, it immediately occurred to Dutrochet 

 that the reaction of the membrane on its con- 

 tents might be strong enough to raise to a 

 sensible elevation the fluid diluted by the water 

 which was absorbed. This conjecture was com- 

 pletely verified by a variety of experiments, of 

 which the following is the most striking. The 

 coecum of a chiclcen filled with a solution of 

 gum, in five parts of water, was fixed on one 

 end of a glass tube open at both extremities, 

 twenty-four inches long, and a fifth of an inch 

 diameter, and was then immersed in rain water. 

 The fluid gradually rose in the tube at the rate 

 of an inch per hour ; and in twenty-four hours 

 flowed over the upper orifice. Here, therefore, 

 is an exact representation of the ascent of the 

 sap, by the impulse communicated to it from the 

 spongioles of the roots. This discovery enabled 

 him to construct an instrument which might 

 serve as a measurer of the power of endosmose. 

 This consists of an inverted funnel and tube, 

 the latter of which is furnished with a scale, 

 while the mouth of the funnel is covered with 

 a piece of bladder, or other organic membrane ; 

 and which is supported on a plate of metal, 

 perforated with many holes. The fluid to be 

 tried as a syrup, for instance, is poured into the 

 inverted funnel, the tube is then fitted into the 

 throat of the funnel by means of a cork, and the 

 covered mouth of the funnel is immersed a little 

 under the surface of a glass of rain water, in a 

 tube forty inches long, and a twelfth of an inch 

 in diameter ; the fluid will rise at the rate of 

 about six inches per hour and in seven hours 

 will flow over the top. 



All fluids having a greater density than water, 

 consequently all the organic animal and vege- 

 table fluids, such as albumen, milk, solution of 

 gum, gelatin, extract syrup, urine emulsions, 

 &c., are exciters of endosmose. Various sub- 

 stances have the same power, by virtue of dif- 

 ferences in chemical nature, as nitric, acetic, and 

 muriatic acids, potass, ammonia, and alcohol, 

 the two latter being lighter, and less dense than 



water. Sulphate and muriate of soda are also 

 powerful exciters, even in very minute quantities. 

 Certain fluids, however, appear quite inactive, 

 although only two such have been well ascer- 

 tained, and these are sulphuric acid, and sul- 

 phuretted hydrogen. Water impregnated with 

 sulphuric acid excites no action, and if even a 

 moderate portion of this acid be added to an 

 active fluid, such as gum, the endosmic action 

 of the latter is destroyed. Tlie same facts are 

 observed very remarkably in the instance of 

 sulphuretted hydrogen. Thus, water containing 

 a twentieth of its weight of gum, excites power- 

 ful endosmose, but the solution has no action at 

 all if there be also added to it a 200th part of 

 hydrosulphuret of ammonia. Hence, foecal 

 matters do not excite endosmose. Hence, too, 

 the various animal fluids formerly mentioned, 

 cease to excite it as soon as they begin to putrify, 

 because they then all evolve sulphuretted hy- 

 drogen. Accordingly, when an experiment in 

 which endosmose has been produced, is con- 

 tinued till the fluid putrifies, it rapidly sinks in 

 the tube till the internal and external fluids are 

 on a level. 



All organic membranes permit of the processes 

 of endosmose, and exosmose, or as Dutrochet 

 terms it, are active. Of inorganic substances, 

 porous clay, minerals, as a thin layer of gTay 

 slate burnt, or a piece of baked clay, are also 

 active. Through a structure of baked clay, one 

 twenty-fifth of an inch thick, endosmose takes 

 place almost as actively as through an organic 

 membrane ; and it is perceptible, even through 

 a plate three-fifths of an inch thick. Silicious 

 minerals, on the contrary, have very little ac- 

 tivity, and calcareous are quite inactive. All 

 active substances become inactive when they 

 have been penetrated by inactive fluids, as when 

 clogged up by sulphuret of ammonia; but on 

 this matter being washed off, they again rosiune 

 their activity. Active membranes are rendered 

 after a time inactive by all fluids, except those 

 derived from organic sources ; although at fu'st 

 inorganic mixtures may stimulate, and increase 

 this endosmose, yet the velocity soon decreases, 

 and stops altogether at last. The velocity of 

 action differs according to the different densities 

 and temperatures of tlie fluids, the force or im- 

 pulses also varying. With a syrup fonned of 

 equal parts of sugar and water, the force is cal- 

 culated as equal to a pressure of four atmos- 

 pheres and a half. Dutrochet is of opinion that 

 the cause of this ascension of fluids is due to the 

 agency of electricity. The first hint which led 

 him to this conclusion, was taken from some 

 experiments of M. PoiTet, who found that if a 

 vessel was divided into two compartments, by a 

 partition of bladder, and one was fiUed with 

 water, while the other contained only a few 

 drops, the water was impelled through tl^e 



