6 GENERAL AND PHYSICO-CHEMICAL. 



weaker solutions are called hypotonic, and stronger hypertonic. DE 

 VBIES, with the aid of equal cells (cells of the epidermis of the lower 

 side of the leaf of the Tradescantia discolor) has, for various substances, 

 determined the concentration of this limit solution. It was found that 

 the limit solution of analogously constructed salts had the same molec- 

 ular concentration. Thus the alkali salts of the type NaCl (haloid 

 salts, nitrate, acetate) plasmolyzed at one molecular concentration and 

 the salts of the type Na2S04 (sulphate, oxalate, diphosphate, 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.* 



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 concentrations 

 of the same salt, all solutions whose concentration lie below a certain 

 limit cause the exudation of haemoglobin. On comparing the molec- 

 ular 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 molecular concentration of the plasmolytic 

 salt solutions. From this it probably follows that the protective action 

 of the salts upon the blood corpuscles depends upon the same reason 

 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 haemoglobin. Those bodies, on the contrary, 



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



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



' Arch. f. (Anat. u.) Physiol., 1888, p. 31; Zeitschr. f. Biol., 26, 414, (1889). 



