1922] McDonald: On Balantidium coli and Balantidium suis 261 



a specific character. Attempts to discriminate between the two forms 

 on the basis of cytopyge or vacuoles were without result. 



The specific differences just discussed have seemed to indicate a 

 sufficient degree of separation of the two types to warrant iho~ division 

 of the ciliates of the genus Balantidium which occur in the pig into 

 two distinct species. The description by Malmsten (1857), in con- 

 junction with the figures (Malmsten, pi. 1, figs. 1-6) which he pub- 

 lished, make it practically certain that the ovoid type is the one 

 originally described by him and to which he gave the name Para- 

 moecium (?) coli. 



So far as I have been able to determine, the elongate species above 

 described has never before been distinguished from Balantidium coli. 

 For this new species I suggest the name Balantidium suis. As a sum- 

 mary of the specific characters discussed above I give the following 

 description : 



Balantidium suis sp. nov. Body elongate; length approximately 

 twice the breadth and varies from 35 to 120/* ; breadth from 20 to 60/x ; 

 usually tapers more posteriorly, is blunter anteriorly, longest diameter 

 transects longitudinal axis anterior to its midpoint ; adoral region ven- 

 trally placed, cytostome % of way posteriorly along ventral surface; 

 nucleus rod or sausage-shaped, at least one-half the length of the entire 

 organism, its width about one-fourth of its length ; the species is para- 

 sitic in the pig. 



The specific name, Balantidium suis, seemed fitting since it indi- 

 cated the common host, Su$ scrofa. Whether or not this species occurs 

 in man it has not been possible to determine conclusively. A review 

 of published case records of balantidiasis seems to show that it does 

 not, but only a few of these records are accompanied by figures or 

 descriptions of the organisms which are adequate for making positive 

 discrimination. Fortunately, I have been able in two cases to make 

 some direct observations. 



Through the kindness of Mr. W. H. Barnes, of the Department of 

 Pathology of the University of California, I was permitted to study 

 sections of the human intestine which he had obtained at an autopsy 

 following a fatal attack of balantidiasis. Imbedded in the serous and 

 subserous layers were numerous balantidia. Measurements to show 

 proportions were of little value under the conditions, for the form 

 of each organism was largely determined by pressure, exerted by sur- 

 rounding tissues. But from other characters, the type of nucleus 

 especially, it was conclusively determined that the species there present 

 was Balantidium coli. No individuals of Balantidium suis were found. 



