Researches on the motion of the juices in the animal body : and the effect of evaporation in plants : together with an account of the origin of the potato disease, with full and ingenious directions for the protection and entire prevention of the potato plant against all diseases / by Justus Liebig ; edited from the manuscript of the author by William Gregory.

  • Liebig, Justus, Freiherr von, 1803-1873.
Date:
[1850?]
Catalogue details

Licence: Public Domain Mark

Credit: Researches on the motion of the juices in the animal body : and the effect of evaporation in plants : together with an account of the origin of the potato disease, with full and ingenious directions for the protection and entire prevention of the potato plant against all diseases / by Justus Liebig ; edited from the manuscript of the author by William Gregory. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    lustre. The fibrine and the cartilages of the ear, which desiccation had rendered horny and transparent, again become milk-white and elastic. The power which the solids of the animal body possess of taking up water into their substance, and of being penetrable to water, extends to all fluids allied to water, that is miscible with it.* In the dried state, the animal solids take up fluids of the most diverse natures, such as fatty and volatile oils, ether, bisulphuret of carbon, &c. This permeability to fluids is possessed by animal tissues in common with all porous bodies; and no doubt can be entertained, that this property is determined by the same cause which produces the ascent of fluids in narrow tubes, or in the pores of a sponge ; phenomena, which we are accustomed to include under the name of capillary action. One condition, essential to the permeability of porous bodies for fluids (or their power of absorption), is their capability of being moistened; or the attraction which the particles of the fluid and the walls of the pores or tubes have towards each other.! A second condition is the attraction which one particle o-f the fluid has to another. We have no means of estimating the absolute size of the particles or molecules of a fluid, such as water, but they are certainly infinitely smaller than the measurable diameter of a tube, or of the pores of a porous body. It is obvious, therefore, that in the interior of a capillary tube or pore, filled with a fluid, only a certain number of the fluid molecules are in contact with the walls of the tube, and attracted by them ; while in the middle of the tube, and from thence towards its parietes, fluid molecules must exist which only retain their place in virtue of the attraction which the molecules, attracted by the parietes, exert on those not so attracted; that is, by the cohesive attraction of the fluid. Liquids flow out of capillary tubes, which are filled with them, only when some other force or cause acts, because capillary attraction cannot produce motion beyond the limits of the solid body which determines the capillary action. The penetration of a fluid into the pores of a porous body, is the result of capillary attraction; its expulsion can be affected by a mechanical pressure; and may be accelerated by increasing this pressure, and by all such causes as diminish the mutual attraction of the fluid molecules, or the attraction of the walls of the pores for those molecules. The condition most favorable to the passage of a fluid through the pores of a porous substance under pressure, is when one fluid molecule can be displaced so as to glide away over another. The slightest pressure suffices to expel the displaceable particles of water from a sponge; a higher pressure is required to express the same fluid from bibulous paper ; and a pressure much higher still is necessary in order to cause water to flow out of moist wood.J We may form some idea of the force with which porous organic substances, such as dry wood, absorb and retain water, if we remember, that by inserting of wedges of dry wood in proper cuts, and subsequently moistening them, rocks may be split and fractured- When we compare with the properties just enumerated, which belong to all porous bodies, those properties which are observed in animal substances under the same circumstances, it appears plainly that these animal substances have pores in certain directions ;§ although these openings are so minute that they are not, in the case of most tissues, perceptible, even with the aid of the best microscopes. It has been mentioned that tendons, ligaments, cartilages, &c, contain, in the fresh state, a certain amount of water, which, according to all experiments made on the subject, is invariable ; and that several of their properties depend on the presence of this water.|| (Chevreul.) When these substances, wrapped in bibulous paper, are subjected to a powerful pressure, a certain proportion of this water is expelled. Fresh and flexible vessels lose, in this way, 37.6 per cent., and the yellow liga- ments of the vertebrae lose 35 per cent, of water. This property, namely, that °of losing water under pressure, is only found in porous substances. It is obvious that by pressure, that is, by diminution of the size of the pores, only that portion of ♦The tissues-absorb other fluids. -f-The moistening of porous bodies. JProdigious force with which porous bodies absorb water. $ Animal tissues are porous. U Amount of water expelled by pressure from tissues.