OSMOTIC PRESSURE. 31 



was found that the limit solution of analogously constructed salts had 

 the same molecular concentration. Thus the alkali salts of the type 

 NaCl (haloid salts, nitrate, acetate) plasmolyzed at one molecular con- 

 centration and the salts of the type Na2SO4 (sulphate, oxalate, diphos- 

 phate, tartrate) at another concentration. If the plasmolyzing power 

 of a molecule of the first group is equal to 3, then the molecule of the 

 second group equals 4. The concentration of the limit solution varied 

 in DE VRIES' experiments between the limits corresponding to a NaCl 

 solution of 0.6-1.3 per cent. 



As above mentioned, only those substances bring about plasmolysis 

 which cannot themselves pass through the protoplasm envelope of the 

 cell content, and these substances only in the case that the concentration 

 is sufficient. If a body is taken up by the protoplasm it produces no 

 plasmolysis, because its tendency to attract water has been satisfied 

 by its own passage into the cell. These substances do not produce 

 plasmolysis in any concentration. If a body slowly passes in, then 

 at first it causes plasmolysis, but this then ceases later. The plasmolytic 

 methods have been used by DE VRIES, and especially by OvERTON. 1 



Experiments with Blood Corpuscles. Over a hundred years ago 

 HEWSON observed that the blood corpuscles were destroyed in water, 

 and that salts in certain concentrations prevented destruction. 2 HAM- 

 BURGER 3 has carefully and systematically investigated the action of 

 salts of the alkalies and alkaline earths, and concludes that when blood 

 is mixed with certain volumes of solutions of different concentra- 

 tions of the same salt, all solutions whose concentration lies below a 

 certain limit cause the exudation of haemoglobin. On comparing the 

 molecular concentration of the limit solution of different salts it was found 

 that they bore the same relation to each other as the relative figures 

 found by DE VRIES for the osmotic action. From this it probably fol- 

 lows that the protective action of the salts upon the blood corpuscles 

 depends upon the same reasons as the plasmolysis. This conclusion 

 is also supported by the fact that those substances which, according 

 to DE VRIES, in proper concentration cause plasmolysis in living plant 

 cells, can also under similar conditions prevent the exudation of haemo- 

 globin. Those bodies, on the contrary, which do not cause plasmolysis, 

 act in aqueous solution in the same manner upon the blood corpuscles 

 as pure water. This has been especially shown by the investigations 



Of GRYNS. 4 



Different investigators have attempted to perform plasmolytic 



1 Vierteljahrschr. d. Naturf. Gesellsch. zu Zurich, 40, 1, 1895; 41, 383, 1896. 



2 Phil. Trans., 1773, p. 303. 



3 Arch. f. (Anat. u.) Physiol., 1887, p. 31; Zeitschr. f. Biol., 26, 414, 1889. 



4 Pfliiger's Arch., 63, 86, 1896. 



