430 ' GENERAL PHYSIOLOGY 



chevsky, Metschnikoff and others, chemotaxis has now become 

 recognised as a phenomenon of wide distribution among free-living 

 cells and of extraordinary significance, not only for unicellular 

 organisms but also for life in the cell-community. 



Among naked protoplasmic masses chemotactic phenomena were 

 first observed by Stahl ('84) in Myxomycetes. He allowed the 

 yellow reticulate plasmodium of ^thalium septicum, which lives 

 upon tan, to creep upon moist strips of filter-paper, and then hung- 

 up the strips with one end in water that was deprived of oxygen 

 and shut off from the oxygen of the air by a layer of indifferent 

 oil, while the other end was in contact with the air. The result 

 was that the protoplasm of the strands that dipped into the water 

 gradually streamed completely out and accumulated above the 

 layer of oil upon the moist filter-paper in the air. Hence it was 

 positively chemotactic to the oxygen of the air. That it was not 

 the water itself which the plasmodia sought to avoid, as might 

 perhaps be supposed, follows from the fact that the plasmodia are 

 positively chemotactic to water and always creep from dry to 

 moist, thus manifesting a specific hydrotaxis. The strips of 

 filter-paper in the experiment must always be kept moist, in order 

 that the chemotaxis toward water may not interfere with that 

 toward oxygen. The plasmodia behave chemotactically toward 

 other substances also, especially the tan that serves them as food. 

 Thus, in Stahl's experiments the protoplasmic masses always crept 

 toward pieces of tan or toward little balls of paper that were 

 soaked with an extract of tan, and collected there, a form of positive 

 chemotaxis which Stahl termed trophotaxis because it plays an 

 important rdle in the habit, which is wide-spread among unicellular 

 organisms, of searching for food. Leber ('88), Massart and Bordet 

 ('90), Metschnikoff ('92), Buchner ('90), and others have discovered 

 chemotactic properties in the leucocytes of vertebrates, and a 

 relation has been found here that is of the greatest importance 

 with respect to the behaviour of organs toward infectious diseases. 

 As has already been seen, 1 Bacteria excrete certain metabolic 

 products, such as the toxines, which recently have attracted greatly 

 the attention of investigators. These products exercise upon 

 leucocytes a very pronounced chemotactic effect, and cause them 

 to creep in great swarms to any place in the organism where 

 Bacteria have entered and multiplied. At the place of infection a 

 dense accumulation of leucocytes takes place and in certain cases, 

 as Metschnikoff has shown, they devour the bacteria and determine 

 in part the further course of the infection (Of. Fig. 210). If the 

 bacteria are not present in too great numbers, they may succumb 

 in the struggle with the leucocytes, which latter in a certain sense 

 represent the police of the body in comparison with the weaker 

 intruders, and the infection is stopped. If the bacteria prove the 



1 Cf. p. 175. 



