CHAPTER I 



The Protozoans 



{Phyhim Protozoa^ 



Radiolai'ians, a paramecium (upper cen- 

 ter) and three flagellates 



Th 



.HE protozoans belong to a microscopic world 

 into which we may peer, but only through a glass 

 daricly. We have no hope of coming face to face with 

 the problems of their microcosm because our faces 

 are too big and our sense organs are scaled accord- 

 ingly. This difference in size, however, does not de- 

 ter the protozoans from entering very importantly 

 into the natural economy of which we are a part, or 

 from invading our bodies and living there as para- 

 sites or as uninvited commensal guests that share 

 the organic matter we ingest. For many thousands of 

 years men have been dying of protozoan-caused 

 amebic dysentery and African sleeping sickness. The 

 Roman Empire is often said to liave fallen victim 

 not so much to political events as to the protozoans 

 that cause malaria. Again and again epidemics of 

 protozoan-caused disease have returned to decimate 

 the animals that man has taken into his economic 

 household, causing widespread distress among those 

 who tend silkworms, honeybees, or domestic flocks 

 and herds. Yet the microscopic organisms — at least 

 100,000 kinds of them, protozoan and otherwise, 

 and many of them occurring on everything men 



touched or ate — went unknown and unsuspected 

 during almost all of man's long history on earth. 



Then, in 1674, a minor Dutch official named 

 Leeuwenhoek trained a simple lens of his own mak- 

 ing on some water from a small inland lake near his 

 home in Delft and became the first to observe and 

 describe living protozoans. 



By 1816, when Baron Cuvier was putting together 

 Le Regne Animal, the first important modern work 

 on animal classification, he had to write in his pref- 

 ace that "infusorians, oft'ering no field for anatomical 

 investigations, will be brielly disposed of." By in- 

 fusorians he meant protozoans and rotifers (p. 137), 

 because they were the most numerous of the micro- 

 scopic forms to be found in infusions, standing water 

 containing decaying organic matter. He disposed of 

 the infusorians in two and one-half pages in a book 

 that ran to about two thousand. Today our knowl- 

 edge of protozoans is a major branch of biology and 

 fills many hundreds of published volumes. The in- 

 troduction of achromatic lenses for the microscope 

 has made it possible to see the detailed structure of 

 Leeuwenhoek's "very little animalcules," whose ex- 



16] 



