244 University of California Publications in Zoology [VOL. 20 



PAGE 



Adoral ciliary rootlets 286 



Radial fibers . 286 



Discussion 288 



Summary 293 



Literature cited , 294 



Explanation of plates 298 



INTRODUCTION 



The earliest observation of Protozoa of the genus Balantidium has 

 in several instances been accredited to Antony von Leeuwenhoek 

 (1708). During an attack of dysentery he detected motile organisms 

 in the discharges. At that time no discrimination had been made 

 between ciliated and flagellated protozoa and his account of his obser- 

 vations is not sufficiently complete to make possible the classification 

 of the organisms which he found. However, he stated that they were 

 about the size of red blood corpuscles, which would indicate that they 

 were intestinal flagellates and not Balantidium, which is very much 

 larger. 



Malmsten (1857) was the first to describe Balantidium coli. This 

 species has become better known than the other species of the genus, 

 due to its being the cause of a specific dysentery known as balantidiasis. 

 Two persons suffering from this disease came to Malmsten for medical 

 attention during 1856-57. Pie was assisted in the study of protozoans 

 which he found in the excreta from these two patients by the zoologist 

 Loven who believed that the parasites were new to science and so pre- 

 pared a careful description of them accompanied by figures. For the 

 organism they suggested the name Paramoecium ( ?) coli. Since that 

 time infections with Balantiddum coli have been reported in increasing 

 numbers and some cytological studies 'have been made, though much 

 more attention has been given to the problems of prophylaxis and 

 treatment of the disease which this species causes than to the parasite 

 itself. 



The first record of Balantidium coli as a parasite of pigs was made 

 by Leuckart (1861). Stein (1862) also studied these forms from pigs 

 and he was the first to assign them to the genus Balantidium. The 

 genus had been established by Claparede and Lachmann (1858) with 

 Balantidium entozoon from the frog as the type species. More recently 

 Strong (1904), Brumpt (1909), Walker (1913), and others have car- 

 ried on investigations on this parasite of pigs in order to become 

 acquainted with the problems involved in the infection of man. 



