198 PROTOZOAN PARASITISM 



tion, the excretory pore, through which the waste 

 products are cast out. 



The macronucleus, the large somatic nucleus, lies 

 deep in the central part of the body, is bean shaped, 

 and close to it, in the depression, lies the small micro- 

 nucleus. 



The whole body of the organism is somewhat pear- 

 shaped, the smaller end being anterior. It is of 

 fairly constant shape but is somewhat plastic and may 

 show some degree of flexion and elongation in forc- 

 ing its way through compact solid materials. 



Those who have httle or no opportunity to study 

 these parasitic organisms, will be able to familiarize 

 themselves with the general form and thereby avoid 

 confusion with the flagellates by studying the com- 

 mon free living kin, Paravieciuin, in pond water or 

 grass infusion. 



BALANTIDIUM COLI 



The most common cihate of man's intestine, and 

 the most conspicuous in size, is Balaiitidiuin coli, 

 discovered by Malmsten in 1856 in two patients with 

 dysentery in Stockholm. This is the only one fa- 

 miliar, even by name, to any considerable number of 

 physicians or medical laboratorians. 



At that it is not a common parasite. While it 

 has been reported of world wide distribution, and is, 

 by Walker's (1913) report, relatively common in the 

 Philippine Islands, it is a rare parasite of man in this 

 country. Craig notes that it has been seen in man 



