XXI] PATHOGENIC ORGANISMS 565 



that chemical substances either attract or do not attract 

 leucocytes. Thus, for instance, Massart and Bordet found 

 the lactic acid acting powerfully — negative chemiotaxis ; 

 Buchner found collagen, alkali albumen, gluten casein 

 acting powerfully — positive chemiotaxis. Now, Buchner 

 argues, and I think with justice (Centralbl. f. Bakt. nnd 

 Parasit., x. 22 and 23), that when in an insusceptible 

 animal leucocytosis does occur at the seat of inoculation 

 this leucocytosis is not an expression of the commencing 

 battle between the microbes and the leucocytes, as is main- 

 tained by Metchnikofif and his followers, but is due to a 

 positive chemiotactic action on the part of the bacteria 

 (dead or alive), by which the leucocytes are attracted. 

 Extensive leucocytosis (suppuration) has been shown by 

 Koch to occur after injection of tuberculin containing the 

 products of the tubercle bacilli previously killed ; suppura- 

 tion (miliary abscesses) has been produced by Prudden and 

 Hodenpel in the rabbit after injection into the vascular 

 system of the substance of the tubercle bacilli, previously 

 sterihsed ; also inserting sterihsed tubercle culture by means 

 of capillary glass tubes into the subcutaneous tissue of the 

 rabbit proves positive chemiotactic attractions of the dead 

 bacilli towards leucocytes. This chemiotaxis is brought 

 about by substances— protein — derived from the bacteria 

 themselves, and is dependent on the previous inimical action 

 on the bacteria by the tissue per se. Where the tissue per se 

 possesses this action the bacteria are either only weakened or 

 destroyed, and only under this condition does their sub- 

 stance — protein — become available to attract the leucocytes ; 

 in such cases the weakened and also the killed bacteria are 

 easily taken up by the leucocytes, and these then help to 

 remove them. Under this theory the phagocytosis observed 

 at the seat of the inoculation is therefore dependent on the 



