210 INFLAMMATION 



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 Amoeba. 1 

 In passing may be mentioned the thigmotaxis or thigmotropism 

 (reaction to mechanical stimuli) shown by spermatozoa, which 

 explains their apparently difficult feat of advancing in opposi- 

 tion to the cilia of the epithelium lining 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 Crustacea) 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 experi- 

 ments, which 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. 2 Motile 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 3 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 distant vessels, not in an 

 irregular manner, but all moved directly toward the point of 

 infection, where they collected. As dead cultures of staphy- 

 lococci produced a similar, although less marked, accumulation 

 of leucocytes, he sought the chemotactic substance in their 

 bodies, and isolated a crystalline, heat-resisting substance, 

 phlogosin, which attracted 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 



1 For full details see Jennings (Publication No. 16, Carnegie Institute, 

 Washington, 1904) ; also J. Loeb, "Studies in General Physiology." 



2 Barratt (Zeit f. allg. Physiol., 1904 (4), 87), however, was unable to dem- 

 onstrate that quantities of acids and alkalies just sufficient to kill paramoecium 

 produced any change in the reaction of their protoplasm great enough to be 

 detected by stains or by indicators, although it is well known that much smaller 

 quantities exert marked chemotactic effects. 



3 Fortschritte der Med., 1888 (6), 460. 



