288 Dr. Barry's Account of the Discoveries of Keber 



After the numerous proofs furnished by experiment as well as 

 through logical conclusions, all acquainted with physics and 

 physiology had long considered the porosity of solid bodies as 

 an established fact. My object was to give optical demonstra- 

 tion of the same. Of the methods I pursued, and the results 

 thereby obtained — which to physiology and the practice of medi- 

 cine may not be unimportant — the present communication is 

 intended to give a short outline. 



That porosity is a universal quality of bodies, i. e. that bodies 

 do not entirely fill the space they take up, but enclose interstices 

 between their particles, is properly adopted in physics as an 

 established fact. Any compendium of physics may be referred 

 to in proof of this. To cite merely one of the most striking 

 examples, I remember an experiment instituted by the Acade- 

 micians of Florence in 1661. A hollow sphere of gold having 

 been filled with water, was exposed to strong pressure, when its 

 whole surface became covered with minute drops, like those of 

 dew. Since then the experiment has often been repeated with 

 different metals, and always with the same result. Now, gold 

 being one of the densest bodies, still less can the finely porous 

 structure of others be filled up. Thus it is known that stones 

 which have lain for a long time at the bottom of rivers or the 

 sea, are in their interior more or less moist. 



The porosity of all animal and vegetable textures follows from 

 their name ; for as every texture consists of a network of vari- 

 ously twisted threads or filaments, the organic parts of textures 

 must consequently have interstices. That such is really the 

 case, daily experience shows. Thus wood steeped in water 

 increases in weight and volume; while, on the contrary, wood 

 lying in the air, with dry weather dries up, and with wet 

 weather swells. Further, by means of atmospheric pressure, 

 mercury may be pressed through dense woods, &c. 



What especially concerns animal membranes, — the membrane 

 of the cell, the epidermis, the mucus and vascular membranes, — 

 is the penetrability of the same for gases and liquids ; which, 

 since the application by Dutrochet to the process discovered by 

 Parrot and Fisher of the expressions Endosmose and Exosmose, 

 has been an established and universally adopted axiom. Whether 

 by these expressions is to be understood, as by most natural 

 pnilosophers, merely imbibition and diffusion, the effect of 

 capillary attraction, or whether peculiar properties are to be 

 vindicated for them, which it has lately been attempted to de- 

 duce from the chemical nature and the mechanical constitution 

 of the membranes themselves*, is for our purpose a matter of 



* Justus Liebig, Untarsuchungen uber einiye Ursachen der S'dftebeweyuvy 

 im thierischen Organismus, 1848, pp. 68, 59. 



