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THE BRITISH NATURALIST. [September 



this disease of the Daphniae may be summed up as a struggle 

 een two living organisms, the parasitic cells and the phagocytes." 



Equally suggestive is the battle which takes place in Erysipelas — 

 an inflammation of lymphatic capillaries due to the presence of 

 streptococci. Of this, MacFarland, in an interesting paper on " Sus- 

 ceptibility and Immunity,"* gives the following graphic account: 

 " At the edge of an erysipelatous patch a most active warfare is 

 I eing waged between the streptococci and the cells. Near the 

 centre of the patch there are many free streptococci and also a 

 great many streptococci enclosed in cells (leucocytes), which are, 



r the most part dead. Further out we find hosts of active living 

 cells engaged in eating up the enemies as fast as they can. The 

 phagocytologists tell us that at the centre the bacteria are fortified, 

 actively growing and virulent. In the next zone, the leucocytes 

 which have feasted upon the bacteria are poisoned by them. Out- 

 side, the cells which are more powerful and are constantly being 

 reinforced are waging successful warfare against the streptococci. 

 In this manner the battle continues — the patch spreading when the 

 phagocytes have to yield — or, on the other hand, the disease being 

 arrested when the phagocytes are victorious. 



•In injuries again, say in the case of an open wound to which 

 germs may easily gain access, at the very outset these germs meet 

 with phagocytes ; if these are sufficiently numerous and powerful 

 they defeat the microbes, and the Wound heals up quietly and 

 readily — but if the germs flourish and get beyond the line of defence, 

 they enter spaces between connective tissue elements and so reach 

 lymph channels along which they travel to the nearest lymphatic 

 glands. Here a second line of defence is encountered, and since the 

 phagocytes in lymphatic glands are numerous and active the conflict 

 is a severe one — the accumulation of dying combatants constituting 

 an abscess — whilst in the surrounding region living phagocytes are 

 resisting further invasion ; failing in this, the invading germs make 

 further progress and passing on enter the blood stream. The general 

 effects on the invaded individual become more pronounced, as is 

 evidenced by " fever." There is, in short, a condition of blood- 

 poisoning, the febrile symptoms being a further effect of the conflict 

 between leucocytic phagocytes and the aggressive micro-organisms. 



Under more normal and healthy conditions Phagocytosis will prob- 

 ably be studied with greater interest by the naturalist in connection 

 with the metamorphoses of Batrachians, the absorption of structures 

 which have become functionally useless being apparently due to the 

 action of phagocytes. 



*" International Medical Journal/' Jan., 1894. 



