In concluding this brief but, we hope, useful study of a few selected cells, we may say that an eminent English physiologist has made the statement that a student who has not looked through the microscope and observed the circulation of the blood in the web of a frog’s foot is not fit to study medicine. However beautiful, fascinating and instructive the sight of this circulation may be, we are tempted to make the assertion that the student who has not looked through the microscope at some of the superficial ooze from the bottom of any slow-running stream, in summer, and observed the structure and actions of that wonderful little unicellular animal, the Amœba proteus, is still less prepared to study medicine. In this little speck of protoplasm the problems of life are reduced to their simplest forms, for all higher plants and animals may be regarded as groups of more or less modified amœbæ peculiarly associated together. In our studies of the amœba we will be forcibly reminded of a very clever trick which is practiced in India and is called the mango-trick. In this trick a seed is put into the ground and covered up, and after divers incantations a full-blown mango-bush appears within five minutes. We have never met any one who knew how this thing was done, nor have we ever seen a person who believed it to be anything else than a conjuring trick. So it is with the amœba, a beautiful and fascinating trickster of nature. We understand some of its activities, interesting and exceedingly instructive, but there are many others beyond our ken. We see the commencement and ending of many of its chemical activities, but there are numerous other intermediary processes that take place in the hidden recesses of the protoplasm, and concerning which we know nothing. It may fall to the lot of some reader of this little book, as a patient and keen observer, to unravel some of these mango-like tricks of the amœba or other unicellular creature.