54. 



(9) Other Protozoa. — ^No protozoa other than those just con- 

 sidered have yet been found in the stools of persons who have 

 never Jeft the British Isles. Nevertheless, I think it worth while 

 to point out this obvious fact, as it may direct further attention 

 to the point and possibly induce some workers to bring forward 

 further records or undertake new investigations. 



I would particularly emphasize the fact that no infections with 

 intestinal coccidia or with Balantidiiim appear to have been 

 reported in JBritish residents who have never been abroad. As 

 regards the former, it maj^be noted that there is one British case 

 of supposed coccidiosis of the liver (Silcock, 1890) ; but this is 

 still somewhat doubtful. I have discussed this case elsewhere, 

 in a review of our knowledge of coccidiosis in man (1919 a), and 

 need say no more about it here. Since I wrote this paper, no 

 new facts have, to my knowledge, come to light.' 



As regards Balantldium coli, I would point out that it is 

 somewhat singular that no British cases of infection with this 

 ciliate appear to have been recorded. It is now generally accepted 

 that B. coli is a parasite proper to the pig, from which animal man 

 may occasionally acquire an accidental infection. Swineherds and 

 others particularly associated with pigs are especially liable to 

 balantidiosis. In parts of the British Isles — e.g. in rural Ireland 

 — conditions conducive to infection are apparently not lacking : 

 and one would expect human cases of balantidiosis to occur, from 

 time to time, if the parasite were present in our native pigs. 

 From personal experience I can say confidently that it is. I have, 

 in fact, never examined the faeces of pigs in this country carefully 

 without finding Balantidium present, often in large numbers. 

 It seems, therefore, somewhat remarkable that no human cases of 

 balantidiosis are yet on record — so far as I can ascertain. 



The other intestinal protozoa described from man are at present 

 too little known or too doubtful to merit special individual mention 

 here. 



B. The Spread of Infections in Britain. 



Although much information concerning the incidence of 

 protozoal infections in Britain has now been obtained, very little 

 direct evidence is yet available to show how such infections are 

 spread through the community. Such facts as have been elicited 

 may be briefly mentioned here. 



All the intestinal protozoa of man — with the possible exceptions 

 of Trichomonas hominis and Dientamoeba, whose cysts are still 

 unknown — are probably transmitted from man to man in the same 

 manner. The active forms of all these organisms are capable of 

 living in the intestine, where they multiply by fission. Outside 

 the human body, however, they cannot long survive. They have 



' An English case of intestinal ' ooooidiosis ' has, however, been recently described 

 by Lockhart-Mummery and Gabriel (1919). Through the kindness of Dr. F. G. 

 Crookshank I was able to examine sections showing the structures interpreted as 

 coccidia, and I have no hesitation in saying that tliey were neither coccidia nor any 

 other protozoa ; and consequently that this case was certainly not one of coccidiosis. 



