246 University of California Publications in Zoology [Vol.20 



the small intestine. In the caecum and first three or four feet of the 

 colon the balantidia were always more active and more numerous than 

 elsewhere. Posteriorlj' from this region they were found in progressive 

 stages of encj-stment until in the rectum the majority were completely 

 encysted. 



Occurrence and Geographic Distribution 



Approximately 200 pigs were examined. They had been raised in 

 the Sacramento Valley, except for one lot from Los Banos, California, 

 and a lot from the state of Nevada. Of the 200 pigs examined 68 

 per cent were infected. The examinations were made at nine separate 

 times between September, 1913, and May, 1918, ten to sixty individuals 

 being examined each time. In five of the nine lots every pig was 

 found to be infected. The lowest percentage of infection was 13 per 

 cent, in the lot shipped from Nevada. This indicates a very general 

 infection of pigs with Balantidiiim in this region of the United States. 



Stiles (cit. Strong, 1904), Bel and Couret (1910), and others have 

 previously found the organisms in pigs in the United States. Leuekart 

 (1861), working in Germany, was the first to find Balantidium in pigs. 

 Since then Stein (1862), Eckecrantz (1869), and Prowazek (1913) 

 have reported them from the same country. In 1871 Wising noted 

 their occurrence in pigs in Sweden. Grassi (1882) and Calandruccio 

 (1888) have found the parasites in swine in Italy. Rapclievski (1882) 

 reported the occurrence of balantidia in Russia. In France thej- have 

 been found in pigs by Railliet (1886), Neumann (1888), and Brumpt 

 (1909). Strong (1904), Walker (1913), and several others have 

 noted the occurrence in pigs in the Philippine Islands. Similar reports 

 from China have been made by Maxwell (1912), and Mason (1919) ; 

 from Cuba by Taboadela (1911) ; and from South America by Bayana 

 (1918). These citations indicate that Balantidium coli is probably as 

 widely distributed geographically as is its host, the pig. 



Studies of Living Organisms 



The balantidia are very sensitive to changes of temperature. When 

 the medium in which they are swimming is cooled a few degrees they 

 slow up their movements very decidedly. After a time they become 

 almost perfectly spherical, in which form their activitiy is restricted 

 to a rotary motion with little or no progression. In this condition they 

 will live for six or eight hours at ordinarj^ room temperature. 



