Having thus reached definite conclusions on many points, and having corrected or verified many of the observations of others, so that their findings are reconcilable with my own, I have thought it a not altogether thankless task to record the main results. I have endeavoured, in the following pages, to deal fairly with the work of all my predecessors ; and I have done my best to cope with the immense and scattered literature on amoebae and amoebiasis. I hope I have not omitted to study any previous work of material importance from the zoological standpoint. If so, it is through ignorance of its existence, or ifiability to gain access to it. On the other hand, I have knowingly Ignored much purely medical work ; and for the reason that it is not * A full account of the circumstances here briefly alluded to will be found in the Introduction to Special Report No. 4 (1917), published by the Medical Research Committee. I am glad of an opportunity to acknowledge my obligations to Dr. H. H. Dale, F.R.S., with whom I had the good fortune to work in the early days; to Dr. A. C. Stevenson, of the Wellcome Bureau, who has shared much arduous work wath me throughout, and with whom I have discussed-with much profit to myselfmost of the questions here considered ; and to Dr. G. C. Low, whose extensive clinical experience has always been freely placed at my disposal. For much good advice and frequent assistance in bacteriological matters I am further indebted to Capt. S. R. Douglas, I. M.S. (ret.