65 



and have probably for centuries harboured, an abundance of 

 protozoa. If, at the present moment, a case of amoebic dysentery 

 were discovered in a British household, it is probable that an 

 attempt would be made to trace the origin of the infection to 

 some male member of the family who happened to have been 

 abroad — especially if he had served in the Army and there suffered 

 from 'dysentery'. But it must, in future, be realized that the 

 source of infection is not necessarily the soldier son, returned 

 from foreign parts. It may equally well be the mother of the 

 family, who has never been abroad ; it may be the nursemaid or 

 the cook — with no signs of dysentery about them ; it may be the 

 greengrocer who handles the uncooked vegetables and fruit con- 

 sumed by the family. AH these hitherto unsuspected persons 

 may be passing cysts of E. histolytica and other protozoa by 

 thousands every day. Certain vocations, sojourn abroad, and 

 some other obvious factors are no doubt rightly regarded with 

 suspicion when considering possible sources of infection : but in 

 future suspicion will also fall upon the home circle, and the mere 

 circumstances that a man lives at home, does not work in the 

 sewers, has not had dysentery, and has never been abroad, can 

 hardly be regarded as sound reasons for believing that he is, 

 therefore, not infected with E. Mhiolytica, 



The foregoing points are chiefly for the consideration of the 

 sanitarian, but there is another which is worthy of notice by the 

 statistician also. This is that the figures now obtained offer us 

 a m6ans of checking and correcting certain others which have 

 been previously arrived at. If a body of troops returning home 

 is subjected to protozoological examination, the results obtained 

 can now be more accurately interpreted than has been possible 

 hitherto. For example, if, in such troops, it is found that some 

 10 per Cent, are infected with E. histolytica, it is no longer easy 

 to argue that they have become contaminated abroad ; or that 

 they are importing foreign parasites and thereby threatening 

 danger to the rest of the community. Such a figure would, 

 indeed, be almost devoid of significance, since we now have 

 eviden<3e that the men concerned might have been already 

 infected to a similar extent before ever they set out from home. 

 The earlier records of the incidence of protozoal infections in our 

 retuthing troops will all have to be reinterpreted in the light of 

 the new observations. 



The clinician will probably be more concerned with knowing 

 whether intestinal protozoa cause diseases, and if so, whether 

 these are sufficiently serious to be worthy of his attention. 

 Fortunately, our present knowledge, though imperfect, is able to 

 supply fairly satisfactory answers to these questions. It has now 

 been proved that two of the intestinal protozoa of man are faculta- 

 tively pathogenic — namely. Entamoeba histolytica and Balantidium 

 coli.- The latter has not yet been found in man in Britain (i. e. as 

 an indigenous infection) : the former has, however, been shown 

 to be fairly common in these islands ; and as it can — in certain 

 circumstances — cause dysentery, liver abscess, and other diseases, 



