THE THEORY OF OSMOTIC PRESSURES. 285 



subject of osmotic pressures and cell turgor. Nine years 

 elapsed before the subject was taken up by animal 

 physiologists, and it is only during- the last few years that 

 we have awakened to the importance of Pfeffer and Van 

 t' Hoffs researches and their manifold application to our 

 science. 



Hamburger 1 was the first, at the instigation of Donders, 

 to apply these results to questions in animal physiology. 

 In his first paper on the subject he confines himself to 

 testing on blood-corpuscles the results obtained by De Vries 

 with plant cells, and found that these corpuscles might be 

 used for demonstrating the isotonicity of equivalent salt 

 solutions. Ue Vries compared in different salt solutions 

 the concentration at which the plasmolysis first began to 

 take place. Hamburger found that red blood-corpuscles 

 began to lose their haemoglobin in salt solutions of a certain 

 concentration varying with the nature of the salt. It was thus 

 possible to determine the relative osmotic pressures of two 

 salt solutions by observing how much distilled water must 

 be added to each in order to produce breaking up of the 

 corpuscles and tinging of the fluid by haemoglobin. Ham- 

 burger in this way obtained results much exceeding in 

 accuracy those got by experimenting on vegetable cells. 

 The definiteness of the point at which the breaking up of 

 red corpuscles begins is the more surprising, as Hamburger 

 has shown that the membrane or limiting layer of the red 

 corpuscles is not impermeable or " semi-permeable," in the 

 sense that Traube's membranes are, but that it permits the 

 passage of salts and even of proteids. The transfer, how- 

 ever, of substances from the corpuscles to the surrounding 

 medium is invariably accompanied by a passage of other 

 substances in the medium into the corpuscles, and this 

 exchange always take place in isotonic proportions, so that 

 the tonicity, or osmotic pressure, of the surrounding fluid,, 

 as of the red corpuscles, is unchanged. It would be 

 difficult to give any physical explanation of this curious 

 interchange, and Hamburger is evidently inclined to ascribe 



1 Archiv f. Anat. u. Phvs., p. 476, 1886, and p. 31, 1887, and other 

 papers. 



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