Thus it is evident from a number of various facts, that the eosinophil cells found in the tissues are not formed there, but have immigrated from the blood-stream. It naturally often happens that this appearance is not preserved equally distinctly in all cases. For, as has been seen in the ordinary polynuclear leucocytes, the immigrated polynuclear eosinophils may similarly change to mononuclear cells; they may perhaps settle down, and approximate to the character of fixed connective tissue cells. Such appearances may readily give rise to the view that in this case the reverse nuclear metamorphosis has occurred; that is a progressive development from mononuclear eosinophil to polynuclear cells. In agreement with Goldmann, Jadassohn and H. F. Mueller, we believe that the only admissible explanation for the facts mentioned above is that the eosinophil cells obey specific chemiotactic stimuli. By this hypothesis we can easily understand eosinophil leucocytosis, the presence of eosinophil cells in exudations and secretions, and the local accumulation of this kind of cell. As to the nature of these chemiotactically active substances, we can so far only surmise. From amongst the clinical phenomena capable of throwing light on this subject we mention once more the fact, that the metabolic products of bacteria repel the eosinophil cells. The opposed behaviour of eosinophil and neutrophil cells is very well illustrated by a case of Leichtenstern: "In a very anaemic almost moribund patient with Ankylostomias there were found 72% eosinophil cells in the blood in 1897. The patient contracted a croupous pneumonia, and in the high febrile period of the disease the number of eosinophils sank to 6-7%, and rose again after the termination of the pneumonia to 54%. After removal of the worm the number at once fell to 11%. In the year 1898 the patient harboured but a very few Ankylostomata; Charcot's crystals were no longer present in the faeces; the number of the eosinophils amounted to 8%."