November 3, 1911] 



SCIENCE 



583 



at times to possess the opacity and insolu- 

 bility of a mill-stone; but looking persist- 

 ently and with care into what appears to be 

 a mill-stone not infrequently proves it to 

 be composed of reasonably transparent 

 material. The members of our institute 

 should take somewhat to themselves as pro- 

 fessional men this obscure and difficult 

 problem, and aid in its solution as a matter 

 of their duty to the public. 



DuGALD C. Jackson 



Massachusetts Institute 

 OF Technology 



TWENTY-FIVE YEARS OF OSMOTIC FEES- 

 SURE IN THE MEDICAL SCIENCES'- 



On October 14, 1910, a large number of 

 scientific men met in the lecture room of 

 the Botanical Institute at the University 

 of Utrecht, for the purpose of celebrating 

 the twenty-fifth anniversary of Van't 

 Hoff's theory of "osmotic pressure."^ 

 Professors Ernst Cohen and Hugo de 

 Vries gave the principal addresses. The 

 former, in his most inspiring and fibaished 

 address, pointed out the invaluable services 

 rendered by this great master to the science 

 of chemistry.^ Professor de Vries gave a 

 lecture on vacuoles and on this occasion 

 emphasized the importance of physical 

 chemistry in general and particularly that 

 of the theory of osmotic pressure for plant 

 physiology.* 



^ Translated from the German by E. I. Werber, 

 Baltimore, Md. 



- J. H. Van 't Hoff, ' ' Lois de 1 'equibre ohimique 

 dans I'etat dilue, gazez on dissons, " Kongliza 

 StvensTca VetensTcaps-Akademiens Handlingar, 21, 

 No. 17, October 14, 1885. 



^ Ernst Cohen, "Een Kwart eew moderne 

 Chemie," Chemisch Weelcblad, No. 42, 1910 

 (Dutch); "Ein Vierteljahrhundert moderner 

 Chemie," Zeitschrift fiir Elektrochemie, B. 16, 

 No. 20, 1910. 



* Hugo de Vries, ' ' Vacnolen, Verhandl. v. h. 

 Provincial Utrechtsch," Genootschap van Kunsten 

 en Wetenschappen, 1910, p. 36. 



It would, I venture to say, amount to an 

 unexplainable neglect, if the great body of 

 medical investigators failed to give expres- 

 sion to the strong feeling of gratitude to 

 this great scientist. 



It gives me pleasure to present a brief 

 account of the researches of de Vries and 

 Van't Ho££ and the indebtedness to them 

 of the sciences referred to in the preceding. 



In the first half of the last century it, 

 was already known that many substancess 

 have the power to attract water and also. 

 that this power was of great importance- 

 for the life of plants. In 1844, Mitscher-. 

 lich made the first attempt to determine- 

 quantitatively this attraction. His figures,, 

 however, as well as those of later investiga- 

 tors, were by no means satisfactory. 



As late as 1881 Pfeffer, in his text-book 

 of plant physiology, deplores this fact and 

 points out how important for the study of 

 some of the phenomena of life it would be 

 to know, even if only approximately, the 

 water-attracting force acting in each and 

 every substance contained in a plant cell. 



It was in the year following (1882) that 

 Pfeffer's hopes were fully realized by the 

 great botanist Hugo de Vries, who actually 

 solved the problem.^ He employed three 

 biological methods, of which the plasmo- 

 lytic gave the most reliable results. This 

 method consisted in employing a salt solu- 

 tion strong enough to bring about a slight 

 separation of the contents of the plant cell 

 from the cell membrane, in other words, to 

 induce plasmolysis in the cell. Since this 

 separation of protoplasts (plasmolysis) was 

 due to the fact that the power of the sur- 

 rounding fluid to attract water was some- 

 what greater than that of the cell contents^ 

 de Vries concluded that solutions of other* 



" Hugo de Vries, Proces-Verbal der Konikl^ 

 Akad. von wetenschappen te Amsterdam, October 

 27, 1882; more exhaustively in Pringsheims Jahv- 

 biicher f. wissensch. Botanik, 14, 1884, p. 427. 



