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the whole of the work described in the present papers, but it fails to 
demonstrate finer details properly. Our work must, therefore, be 
regarded as incomplete, and certainly the more important parts of it 
should be repeated by workers using methods more perfect than those 
employed by us. 
A second lesson was that too much of the work done on the 
pathogenic protozoa, particularly by medical men, has been directed 
by conceptions derived from bacteriology. 
Days of tedious searching of slides and of observation of 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 unbiassed 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 apparent y 
antagonistic probabilities obtained by deductions from work done 
along apparently parallel lines of research. Of course, the examina¬ 
tion of fresh preparations should be supplemented by the examina 
tion of stained material. Lastly, at the present moment more is 
known, in every way, of malaria than of almost any other disease, 
observing less studied protozoan infections it will fiequently happen 
that our knowledge of what actually does occur in malaria will lea 
to the formation of an ultimately successful working hypothesis, or to 
the correct interpretation of newly-observed phenomena. 
