The study of the parasitic protozoa is now being so ardently pursued that for the time being bacteria have dropped into the background. The pathogenic trypanosomes, thanks largely to the impetus given by the work of Novy, have been the center of interest for a long time, but other protozoan parasites are rapidly coming to the front. Some of these are proving to be even more difficult to study than the trypanosomes, and we are but slightly advanced in our knowledge of their complicated life histories. Bit by bit, however, the remarkable life cycles are being worked out. Recently Nuttall and Graham Smith1 have made an elaborate study of the infection of dogs with Piroplasma and have reached a number of important conclusions.
Piroplasma, it will be remembered, is a minute intracellular parasite first discovered by Theobald Smith in the blood of cattle affected with Texas fever. Similar parasites,