Immunity in Multicellular Plants 81 



of acquired immunity in these plants has also been demonstrated 

 by Stahl. The following is the passage in his paper referring to 

 this subject, a passage very important from a general point of view 1 : 

 " If we replace the water in a vessel by a 1 or 2 % solution of 

 glucose, we observe either the death of the plasmodia, if the action 

 is too rapid, or merely their retreat from the glucose solution. 

 Even solutions of or % are at first avoided by the plasmodia 

 and, should the action be too rapid, may cause their death. Usually 

 the plasmodia emigrate into those portions of the substratum remote 

 from the solution, to return after some time, often only after several 

 days, and immerse themselves in the solution of glucose as they do 

 in an infusion of tan, although with more hesitancy. Consequently 

 the Myxomycetes accommodate themselves slowly* to a more con- 

 centrated solution, probably by giving up a certain proportion of their 

 water. I was able to observe the same phenomena with even much 

 more concentrated solutions (2 / ). A plasmodium which at the end 

 of several days had adapted itself to a 2 % solution of glucose and had 

 sent out numerous processes into it, found itself injuriously aflfected 

 when the sugar solution was suddenly replaced by pure water. Those 

 that remained alive had retired to a great distance from the upper 

 layer of the fluid and did not descend again until the end of the second 

 day. After a fresh change of fluid we were able to observe first the 

 repulsion and later the attraction of the plasmodia, but a certain time 

 always elapses before the plasmodia become accustomed to the change 

 in concentration. We obtain the same result when we replace a 2 % 

 solution, not by pure water, but by a \ or a 1 /o solution " (p. 166). 



De Bary 8 had already interpreted these facts as being due to an 

 immunity acquired by the plasmodia, the result of an adaptation of 

 these organisms to solutions which they had, at first, carefully avoided. 

 He threw out the suggestion that a similar adaptation might take [34] 

 place in regard to solid substances ingested by the Myxomycetes. 



As these phenomena of acquired immunity, in organisms so 

 primitive and of so simple a structure, are of immense importance 

 from the point of view of Immunity in general I felt bound to submit 

 them to a personal investigation, I found it an easy matter to 



1 [Stahl used plasmodia which had spread themselves on a substratum of wet 

 filter paper applied to the inside of glass vessels, its lower edge touching the surface 

 of the experimental fluid at the bottom of the vessel (Translator).] 



2 The italics are M. Metchnikoff's. 



3 " Vergleichende Morphologic u. Biologic der Pilze, Mycetozoen u. Bacterien," 

 Leipzig, 1" Aufl., 1884 ; also authorised English translation, Oxford, 1887. 



