Bancroftian filariasis and the reticulo-endothelial system

In Bancroftian filariasis the rise and the fall of the microfilarial tide are caused by different mechanisms. There is now anatomical evidence, furnished by O'Connor, that the rise is caused by timed parturition of female worms, and here the significance of spent worms has been imperfectly grasped either as a normal daily event or as a result of their sterilization by drugs. The fall of the tide is caused by the mobile cells of the reticulo-endothelial system, for which statement the line of argument runs thus. When helminths enter the tissues of a host animal, it is these very cells which collect and attack them actively. For Bancroftian filariasis their presence was reported years ago, but their fundamental importance has been missed. They destroy microfilariae in lymph nodes before they get into the blood, and by their accumulation and their development to the end cell of the series, the fibroblast, they cause lymphatic obstruction; the lymph conditions then become those of a culture medium which may be four million times better suited to the haemolytic streptococcus than is normal lymph, and when infection with this bacterium has set in they become still more favourable for growth of fibroblasts and increase of elephantiasis.