256 BALANTIDITJM COLL 



which was, from the sigmoid flexure onwards, filled with stinking pus. 

 At these places but few Infusoria were found, but they were present 

 in immense numbers over the whole of the sound mucous membrane 

 of large intestine, as also in the cpecum and vermiform appendix. 

 There were none to be found either in the small intestine or in the 

 stomach. 



Stein has made it probable that this parasite had perhaps been 

 previously observed, and that by the great discoverer of the Infusoria 

 — Leeuwenhoek himself. The latter at least reports^ that, once 

 having had for a lengthened period abnormal stools, he made an 

 examination of them, and observed delicate mobile organisms, mostly 

 about the size of a blood corpuscle, but some larger, wliich moved about 

 with the aid of a little foot-like hook. In small portions of the fteces, 

 as large as a grain of sand, there was at least one of these little 

 animals, but generally more — four or five, or even eight. These 

 never occurred in the normal excrement. Since the Balantidia are 

 considerably larger than a blood corpuscle, Leeuwenhoek's description 

 seems but slightly applicable ; but probably the report as to the 

 size was based on a merely subsequent estimate, in which a mis- 

 take might easily be made ; and it is indeed impossible that Leeuwen- 

 hoek, with the optical appliances at his disposal, could have seen the 

 movement of cilia, which he describes, in an Infusorian, as only the 

 size of a blood corpuscle. 



The observations of Malmsten still stood alone when I stated, in 

 the first edition of this work (1863), that man was not the only 

 host of the so-called Faramcecium coli, but, on the contrary, that it 

 also occurred in swine, and was in fact found constantly, and in 

 extraordinary abundance, in the colon and caecum of these animals. 

 In order to see the parasites, one has only to take a probe and remove 

 some dung or mucus from the rectum. Even with a lens one can 

 distinguish colourless Infusoria moving here and there about the dung. 



Since my results have been corroborated in various parts of Ger- 

 many, in Sweden (by Stein, Ekeckrantz, and Wising), and in Italy 

 (Grassi), we may conclude that the pig is the proper host of .5a/- 

 antidium coli, and that man only occasionally derives it from the 

 latter, and under favourable circumstances harbours it for a while. 

 In harmony with this is the fact that the Balantidium in man has an 

 average size of 0'06 to 0'07 mm. (according to Wising), which is a 

 little less than that of the forms found in the pig. 



In the meantime, however, the cases investigated by Malmsten 

 have not remained solitary. Stieda^ first observed the occurrence of 



' Loc. cit., Part ii., p. 37. 



