The opening of the text begins with a preface where the author emphasizes the rising importance of protozoa in medical research, particularly as disease pathogens. He observes that while bacteria have garnered attention in recent centuries, the potential significance of protozoa has not been fully recognized, especially in relation to human and animal diseases. He notes the lack of comprehensive literature addressing protozoa as specific disease-causing agents, which motivated him to write this detailed account. The introductory segments also outline the historical context of protozoan research and describe the methods used for studying these organisms, setting the stage for an in-depth investigation of their contributions to various infectious diseases. (This is an automatically generated summary.)