parasites, placed under various conditions, must be spent in studying the pathogenic protozoa, when minutes would almost suffice in the case of bacteria. The difficulty of finding the parasites at all is sometimes extraordinary, and the possible occurrence of a latent infection must never be forgotten.
The study of the pathogenic protozoa must be approached with an unbiased mind and with the remembrance that the known life-cycles of several protozoa are exceedingly complicated. We believe that the continuous observation of living parasites will ultimately furnish the richest reward. A single positive observation so obtained is absolute, and outweighs any number of apparently antagonistic probabilities obtained by deductions from work done along apparently parallel lines of research. Of course, the examination of fresh preparations should be supplemented by the study of stained material. Lastly, at the present moment, more is known, in every way, of malaria than of almost any other disease. In observing less studied protozoan infections it will frequently happen that our knowledge of what actually does occur in malaria will lead to the formation of an ultimately successful working hypothesis, or to the correct interpretation of newly-observed phenomena.
