274 DIFFUSION, OSMOSIS, AND FILTRATION. 



funnel was proportional to the difference of concentration of the solu- 

 tions on either side of the membrane. 



Jolly 1 specially studied the ratio between the amount of water 

 passing into the solution and the amount of dissolved substance passing 

 out, using salts with pig's bladder as membrane. This ratio he termed 

 the endosmotic equivalent of the salt, and maintained that it is constant 

 for the same membrane, concentration of the salt solution, and tem- 

 perature. For some years after this the whole attention of those interested 

 in the matter of osmosis was directed to a fuller study of this ratio in 

 the case of different substances. 2 



As a result of these researches, it was seen that even with the same 

 membrane it was only within slight changes of concentration of the 

 solution that constancy of the endosm<ftic equivalent was obtainable, a 

 result in accordance with expectation, seeing that the physical nature of 

 an animal membrane must necessarily undergo change with the amount 

 of water imbibed, a quantity variable with the concentration of the solu- 

 tions in which it is in contact. With a strictly semipermeable membrane, 

 the endosmotic equivalent is evidently infinite, while the more permeable 

 the membrane to dissolved substance the lower will be the equivalent. 

 Thus, according to Harzer, 3 the endosmotic equivalent for sodium chloride 

 is with fish-swim-bladder, 2 '9 ; ox-pericardium, 4'0 ; ox-bladder, 6 '4. 



It must therefore be admitted that, in spite of the great labour that 

 has been expended on the determination of endosmotic equivalents of 

 different substances with different membranes, the results obtained are 

 of little value to the practical physiologist, who deals with membranes 

 in the living body, whose physical characters are by no means necessarily 

 those of the structures used in such experiments. The only value that can 

 be attached to these determinations is an orienting one, as to the diffusi- 

 bility of the substances into water, through dead animal membranes, 

 under the conditions of the experiments. 



Before we can attempt to answer the question, How is the process of 

 diffusion modified when in an osmose experiment an animal membrane 

 is placed between solution and solvent ? it is obviously necessary to 

 know the physical structure of the membrane. Of this we must admit 

 great ignorance. To Briicke 4 we owe a theory of "pore diffusion." 

 Assuming capillary pores in the membrane, it maintains that, by 

 attraction, a layer of pure water lines these, while an axis of salt solu- 

 tion, whose concentration falls from axis to mantle of the cylindrical 

 pore, lies centrally. The highest concentration in the axis must be that 

 of the salt solution in the experiment, and along the axis ordinary 

 hydrodiffusion takes place, water entering the salt solution and salt 

 entering the water. Along the mantle, however, only water can pass 

 into the salt solution, so that the stream of water exceeds that of salt. 

 If the pores are very narrow, it is conceivable that there is no central 

 core of salt solution, in fact the membrane becomes semipermeable. 



1 Ztschr. f. rat. Med., 1849, Bd. vii. p. 83 ; Ann. d. Phys. u. Chem., Leipzig, 1849, 

 Bd. Ixxviii. S. 261. 



2 Fick, Untersuch. z. Naturl d. Mensch. u. d. Thiere, 1857, Bd. iii. S. 294 ; W. Schmidt, 

 Ann. d. Phys. u. Chem., Leipzig, 1857, Bd. cii. S. 122 ; Beitr. z. Anat. u. Physiol. 

 (Eckhard), Giessen, 1855, Bd. i. S. 97 ; 1860, Bd. ii. S. 1, 31, 147 ; Hoffmann, ibid., 

 1860, Bd. ii. S. 59. 



3 Arch. f. physiol. Heilk., Stuttgart, 1856, Bd. xv. S. 194. 



4 " De diffusione humorum per septa mortua et viva," Berlin, 1842 ; Ann. d. Phys. u. 

 Chem., Leipzig, 1843, Bd. Iviii. S. 77. 



