SLUGS AS MYCOPHAGISTS 235 



gas, and that they make characteristic responses indicating the 

 degree of dilution. Dr. Bartsch also found that man reacts to 

 a dilution of 1 in 4,000,000. Limax maximus, therefore, is much 

 more sensitive to the presence of mustard gas than man. 1 If 

 Limax maximus is thus so extraordinarily sensitive to one gas, we 

 have every reason for believing that it is extraordinarily sensitive 

 to other gases, particularly those which emanate from its food 

 substances such as fungi. If we assume such a sensitiveness, it 

 is not difficult to imagine how it is that Limax maximus finds its 

 way unerringly over a distance of many feet to the fruit-bodies 

 of Phallus, Boletus, Russula, etc., which it devours with such 

 avidity. The sense of smell in slugs, like that in dogs, is doubtless 

 much more acute than in human beings. 



Conclusions. (1) The successful experiments with Phallus im- 

 pudicus, Russula heterophylla, and R. nigricans, described above, 

 clearly show that the fruit-bodies of these fungi, under certain 

 conditions in the open, attract Limax maximus from a distance of 

 at least 10 to 21 feet. 



(2) Having regard to the well-known short-sightedness of slugs, 

 to the fact that slugs find their food at night, and to the sensitive- 

 ness of Limax maximus to mustard gas when diluted to one part 

 in ten million, my observations and experiments lead me to suppose 

 that fungus-eating slugs react at a distance to the odours given off 

 by fleshy fungi, and that in woods and gardens they find the fungi 

 upon which they feed by their sense of smell. 



(3) The chemotaxis of slugs, not merely for fungi but also for 

 garden produce such as lettuce and cabbage, is a subject concern- 

 ing which our information is still very meagre, but which is very 

 amenable to experimental treatment. If the chemotaxis of slugs 

 were sufficiently elucidated, we might perhaps be able to devise 

 much more efficient means for protecting our gardens from the 

 ravages of slugs than any at present known. 



1 Paul Bartsch, " Our Poison Gas Detector and How It was Discovered," 

 Abstract of an Address delivered on February 7, 1920, to the Biological Society 

 of Washington, U.S.A. I read a paper entitled " Upon the Chemotactic Attraction 

 of Fungi for Slugs " at Chicago on December 30, 1920, before the Ecological Society 

 of America. Subsequently Dr. R. F. Griggs called my attention to Dr. Bartsch's 

 work, and then Dr. Bartsch kindly sent me an abstract of his Address. 



