INTRODUCTION 19 



tablished the "lateral-chain" theory and theory of phago- 

 cytosis. These theoretic problems occupied the attention of 

 the workers from 1890 to 1905 and are by no means ended. 

 Laveran, in 1881, had discovered the protozoa of malaria, 

 and in 1903 Button had associated trypanosomes with 

 sleeping sickness. In 1905 Schaudinn, by demonstrating 

 the cause of syphilis to be a protozoon, gave added im- 

 portance to this particular group of micro-organisms, and 

 today investigators are looking in this branch of microbiology 

 for the cause of cancer. 



The serum reactions of Wassermann and Noguchi, the 

 tuberculins and other products of bacterial growth useful in 

 diagnosis and treatment, have interested the whole medical 

 world, and every physician must of necessity be familiar with 

 some part of this knowledge. 



There is hope that the technic and the microscope will 

 receive more attention in the next few years, so that the so- 

 called ultramicroscopic and filterable organisms that are 

 believed to exist will be definitely determined, and also the 

 cause of such epidemic diseases as smallpox and scarlet fever 

 be ascertained. 



