PHYSICAL PROPERTIES OF TISSUES. 65 



branes. 1 It is characteristic of dry, membranous structures; all of 

 which are found to contract, more or less, by the evaporation of moist- 

 ure, and to expand again by its re-absorption; hence the employment of 

 such substances as hygrometers. According to M. Chevreul, 2 many of 

 the tissues are indebted for their physical properties to the water they 

 contain, or with which they are imbibed. When deprived of this fluid, 

 they become unfit for the purposes for which they are destined in life, 

 and resume them as soon as they have recovered it. 



A most important property possessed by the tissues of organized 

 bodies is imbibition; a property to which attention has been chiefly di- 

 rected of late years. If a liquid be put in contact with any organ or 

 tissue, in process of time the liquid will be found to have passed into 

 the areolse of the organ or tissue, as it would enter the cells of a sponge. 

 The length of time occupied in this imbibition will depend upon the 

 nature of the liquid and the kind of tissue. Some parts of the body, 

 as the serous membranes and small vessels, act as true sponges, ab- 

 sorbing with great promptitude; others resist imbibition for a considera- 

 ble time, as the epidermis. 



Liquids penetrate equally from within to without : the process is then 

 called transudation. 



Some singular facts have been observed regarding the imbibition of 

 fluids and gases. On filling membranous expansions, as the intestine 

 of a chicken, with milk or some dense fluid, and immersing it in water, 

 M. Dutrochet 3 observed, that the milk left the intestine, and the water 

 entered it; hence he concluded, that whenever an organized cavity, 

 containing a fluid, is immersed in another fluid, less dense than that 

 which is in the cavity, there is a tendency in the cavity to expel the 

 denser and absorb the rarer fluid. This M. Dutrochet termed endos- 

 mose, or "inward impulsion;" and he conceived it to be a new power, 

 a "physico-organic or vital action." Subsequent experiments showed, 

 that a reverse operation could take place. If the internal fluid was 

 rarer than the external, the transmission occurred in the opposite di- 

 rection. To this reverse process, he gave the name exosmose, or " out- 

 ward impulsion." At times, the term endosmose is applied to the 

 mutual action of two liquids when separated by a membrane; 4 at others, 

 to the passage of the liquid, that permeates the membrane in greatest 

 quantity. 5 



Soon after the appearance of M. Dutrochet's essay, the experiments 

 were repeated, with some modifications, by Dr. Faust, 6 and by Dr. 



1 Roget, art. Physiology, in Supplement to Encyclopaedia Britannica ; and Outlines of Phy- 

 siology, with an Appendix on Phrenology. First American edition, with notes by the author 

 of this work, p. 73, Philad., 1839. 



2 Magendie, Precis Elementaire de Physiologie, 2de edit., 1825, i. 13. 



3 Mem. pour servir a 1'Histoire Anatom. et Physiol. des Animaux et des Vegetaux, Paris, 

 1837; art. Endosmosis, in Cyclopaedia of Anatomy and Physiology, part x. p. 98, June, 1837. 

 See, also, Vierordt, art. Transudation und Endosmose, in Wagner's Handworterbuch der 

 Physiologie, s. 631, Braunschweig, 1848. 



4 Matteucci, Lectures on the Physical Phenomena of Living Beings; translated by Pereira, 

 p. 45, Amer. edit., Philad., 1848. 



6 Poiseuille, Comptes Rendus, xix. 944. Paris, 1844. 

 6 Amer. Journal of the Mod. Sciences, vii. 23, Philad., 1830. 

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