§ 3] CHEMOTAXIS 33 



gather at the margin of the cover-glass, where oxygen is more 

 abundant than elsewhere. If oxidized blood is introduced 

 under the cover-glass, they move toward it, but not toward 

 blood containing much COg in place of oxygen. If green 

 algcB are introduced, the bacteria move towards them so long 

 as they, under the influence of sunlight, are producing oxygen. 

 In the dark the algae have no effect. 



During the decade and a half which have elapsed since En- 

 gelmann's first paper appeared, chemotactic phenomena have 

 been observed among nearly all kinds of motile organisms and 

 with reference to the most diverse kinds of chemical substances. 

 Engelmann ('82) has studied the chemotactic movements of 

 diatoms ; Stahl ('84), of Myxomycetes ; Pebffee ('84, '88), 

 of plant spermatozoids, zoospores, Flagellata, Infusoria, and 

 bacteria ; Aderhold ('88), of Euglena viridis ; Verwoek 

 ('89, p. 107), of Cryptomonas ; Stange ('90), of zoospores and 

 Myxomycetes ; and Massaet ('91), of Spirillum, Heteromita, 

 and Ciliata. 



Within the last five years a voluminous literature has grown 

 up on the medical side relating to chemotaxis in leucocytes and 

 pathogenic bacteria. Into this literature we cannot penetrate 

 deeply, but refer to some of the principal papers : Leber, '88 ; 

 BucHNER, '91 ; RoEMEE, '92 ; Metschnikoff, '92. 



It thus appears that chemotactic phenomena show themselves 

 among all the groups of lower motile organisms : Rhizopoda 

 (Myxomycetes), Flagellata, CUiata, bacteria, diatoms, zo- 

 ospores, and spermatozooids. It can hardly be questioned that 

 the phenomena shown by these organisms are of the same order 

 as those seen in Metazoa — in those ants which Lubbock ('84, 

 p. 238) has shown to move from chemical agents (essence of 

 cloves, lavender water, and other scented stuffs), saturating a 

 camel's-hair brush placed about ^ inch above their path ; and 

 in the larvae of flies with which Loeb ('90, p. 79) has experi- 

 mented. LoEB found that these crept towards a piece of flesh 

 brought nearer to them than the distance of 1.5 cm. Even just 

 hatched larviE (which had therefore never been stimulated by 

 meat) reacted in this way. Not meat only, but a trace of meat 

 juice on glass attracted the larvae strongly. While decaying flesh 

 and cheese allure, neither fat, asafoetida, nor ammonia do so. 



