566 MICRO-ORGANISMS AND DISEASE [cHAP. 



preceding alteration of the bacteria. But in the case of a 

 susceptible animal, that is, when the introduction of the 

 bacteria produces general infection and no local Icuco- 

 cytosis at the seat of inoculation, the bacteria, because they 

 remain vigorous and because they withstand the action of 

 the tissue, do not yield the chemiotactic substance — ■ 

 protein — and therefore no leucocytes are attracted to the 

 seat of the inoculation. 



In connection with the phenomena of chemiotaxis it 

 ought to be borne in mind that just as certain bacteria 

 exert an attraction to the leucocytes, so also is it imaginable 

 that the cells and tissues exert chemical attraction on cer- 

 tain bacteria, just as in the case of Pfeffer's experiments. 

 This at any rate offers a ready explanation of the conspi- 

 cuous attraction that one or the other tissue seems to exert 

 towards certain specific microbes. It is well known that in 

 the acute exanthemata the skin is the tissue which pre- 

 eminently exerts such a positive chemiotaxis on the specific 

 microbes. In anthrax, in typhoid fever, in malaria, in 

 relapsing fever, the spleen has a conspicuous attractiveness 

 for the microbes ; in tuberculosis if is the lymphatic tissues 

 and the spleen. In this disease the lymph-cells seem to be 

 the particular nidus for the growth and multiplication of the 

 bacilli. It is quite possible that the presence of saprophytes 

 in the lymph-cells of the superficial parts of the tonsil, 

 pharynx, and Peyer's glands (Bizzozero, Ribbert, Ruffer) is 

 to be explained in this way, viz., that these cells possess a 

 chemiotactic action, being a more favourable nidus for the 

 growth of the bacteria. 



The conclusion which we think justified in making is that 

 the- phenomenon of mechanical phagocytosis in Metchni- 

 koff's original sense is in some cases unquestionably a sign 

 of weakening and destruction of the microbes, but it cannot 



