Page:Popular Science Monthly Volume 69.djvu/413

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T the present time the importance of protozoa-study is recognized in all branches of biological science where, as single-celled organisms, they illustrate the manifold principles of living things. Thus it is in physiology, in cellular biology, in psychology and in general biology. There is one field, however, a field that is daily growing more extensive, in which the importance of protozoa has only recently been recognized, and this is the field of pathology. To the medical world for the most part, the group of protozoa consists of the few types of parasitic forms that cause human disease, and in this world any one who has a knowledge of Trypanosoma, or Amæba, or Plasmodium, is a student of the protozoa, while a deeper knowledge makes him a biologist. At the present time there are many students of the group in this sense, and the relations of protozoa to human welfare bid fair to be the most popular aspect of protozoan study, while in the public mind already the term protozoa is apparently the synonym of some new and fearsome thing. Commissions for the study of protozoan diseases have been appointed in many countries and chairs for the study of protozoology have been established in the universities of Cambridge and London mainly for the study of the pathogenic forms of these unicellular animals. The present paper deals with a few aspects of this more recent field of protozoa work.

Few pathologists in good standing gave a thought to protozoa until after the malarial organisms had been worked out and the life history completely known through the researches of biologists and surgeons. Thanks to the work of Laveran, Ross, Grassi and Schaudinn, there is no longer a phase in this disease that is unknown, and the relations of the various symptoms of the malady to stages in the life history of the organisms are perfectly established. I do not need to go into the malaria problem, for the life history of the organisms, their relations to the mosquito Anopheles, the coincidence of merozoite 'spore' formation and pyrexial attacks of the disease, are familiar to all who have followed, even remotely, the progress of medical science. I will pass