Reaction of the Phagocytes of Arthropods to their Internal Insect Parasites

Abstract

IN his celebrated work on the pathology of inflammation, first published in 1892, E. Metchnikoff¹ made a general survey of the phenomena of phagocytosis in the animal kingdom and pointed out that there exist between the various groups very striking differences in the behaviour of the white blood cells towards internal parasites. He stated that among the Arthropods the phagocytic reaction is, in general, rather feeble, and suggested that this condition is perhaps related to the development of a chitinous cuticula in these animals, and that since this cuticula prevents the entrance of parasitic organisms the defensive activity of the phagocytes is less marked than in organisms which do not possess this protection. Several years later L. Cuénot, in his “Études sur la physiologic des orthopteres”, criticised the views of Metchnikoff on the ground that the cuticular armature of the Arthropods, in spite of its thickness, is a very inefficient means of defence against parasites. Cuénot had, indeed, observed that the parasites of Arthropods in their habitual hosts are not usually attacked by phagocytes, but he explained this fact on the hypothesis that the parasites have developed the power of resisting the phagocytes, by which they would otherwise be destroyed. According to this idea, when a new parasite arrives in an Arthropod it ought to be attacked by the phagocytes and destroyed by them.