256 IXFLAMMATION, NEGENEKATIOX, GROWTH 



tropism (reaction to light) ; geotropism (to gravity), electropism (to 

 electricity), thigmotropism (reaction to contact), etc. 



The work done upon tropisms applies particularly to ciliated, 

 freely motile organisms, and interests us less in connection with 

 leucocytes than do the observations on such forms as AmcehaJ In 

 passing maj' be mentioned the fhiynwtaxis or thigmotropism (reac- 

 tion to mechanical stimuli) shown by spermatozoa, which explains 

 their apparently difficult feat of advancing in opposition to the cilia 

 of the epithelial lining of the female generative tract. It may also be 

 noted that the nature of reactions of organisms to various stimuli is 

 not constant for even the same organism. Copepods (minute crus- 

 taceae) may be negatively heliotropic in the day and go away from 

 the bright surface of the water, whereas at night the same animals 

 are positively heliotropic and swarm to the surface illuminated 

 brightly by a lantern. Variations in heliotropism may, in some cases, 

 be explained as due to chemical changes that occur in the organism, 

 which explanation is made more probable by J. Loeb's experiments, 

 Avhich show that change in composition in the fluid in which animals 

 are suspended may cause a complete reversal in their reaction to a 

 constant stimulus. IMotile bacteria seem to behave much like ciliated 

 protozoa in their reaction to stimuli. 



CHEMOTAXIS OF LEUCOCYTES « 



That leucocytes come to the site of an infection because of chemical 

 substances produced by bacteria at this point, that is to say, through 

 chemotaxis, was first clearly pointed out by Leber ^ in 1879, who 

 likened the attraction of such substances for leucocytes to the effect 

 of malic acid upon spermatozoids as shown by Pfeffer. He found 

 that in keratitis, leucocytes invaded the avascular cornea from the dis- 

 tant vessels, not in an irregular manner, but all moved directly toward 

 the point of infection, where they collected. As dead cultures of 

 staphylococci produced a similar, although less marked, accumlilation 

 of leucocytes, he sought the chemotactic substance in their bodies, and 

 isolated a crystalline, heat-resisting substance, phlogosin, which at- 

 tracted leucocytes in animal tissues. He also observed that capillary 

 tubes filled with phlogosin or with staphylococci were soon invaded by 

 masses of leucocytes. 



Since Leber's experiments, many other investigations have been 

 made showing that chemical substances of many different origins other 

 than Ijacterial exert a chemotactic influence on leucocytes. Some sub- 

 stances are indifferent in effect, most are positive, while some are be- 

 lieved to repel leucocytes; /. e., are negatively chemotactic. 



7 For full details see .Toiiniii'xs (Publication Xo. 10. Caniotjie tustituto. Wash- 

 ington, l!tn4: also J. Loch, "Studies in (Icncral Pliysiolojiv." 



8 Keview of literature on leucocytes bv TTellv, Krjieb. allix. Patliol., I!tl4 (17,,,), 1. 

 Fortschritte der :\Ied., 1888 (6), 4Gf>. 



