55 



but feeble powers of resistance, and are rapidly killed by drying- 

 and all conditions which differ from those under which they 

 normally live in the bowel. If ingested in the active state by 

 a human being they always perish. In other words, the active 

 organisms can live in the intestine only, and are incapable of 

 playing any direct part in the spread of infections from one host 

 to another. But in certain circumstances — which are not yet 

 properly understood — these active organisms can encyst in the 

 bowel and pass out in the form of more or less resistant cysts 

 with the faeces. It is by ingesting such cysts that a new host 

 becomes . infected. 



It is thus evident that the actual source of infection is^n every 

 case, the person who harbours active protozoa in his gut and 

 passes their cysts in his stools : whilst the spread of infection to 

 other persons is brought about by any or every circumstance which 

 insures these cysts being ingested, while still fresh and living, 

 by another individual. 



It seems reasonable to assume that infections are usually 

 acquired by swallowing food or drink which has been recently 

 contaminated by fresh human faeces containing cysts. This 

 contamination may conceivably occur .in a variety of ways — by 

 the agency of flies, the pollution of water with sewage, or other- 

 wise. The present reports supply no direct evidence bearing on 

 these problems, and it is therefore unnecessary to discuss the 

 various possibilities here. What they do supply, however, is 

 evidence that the contamination of food and drink with fresh 

 human faeces — however it may occur— cannot be uncommon in 

 this country : and it furnishes some suggestive facts which may 

 indicate where the most important foci of infection- should be 

 sought. The evidence for the former conclusion is indirect, and 

 is derived from the demonstration that a considerable proportion 

 of the people of this country has actually acquired infection, in 

 some way, with intestinal protozoa: for the latter inference, the 

 evidence is contained in some observations of Matthews and Smith, 

 which will be briefly considered here. 



These workers (Matthews and Smith (1919), p. 365) ' in order 

 to obtain a closer insight into the actual process of spread of 

 these protozoal infections , . . singled out certain cases, chiefly 

 those [children] infected with E. histolytica, and have examined 

 the whole family of which each one was a member '. They state 

 that ' in only one family ' out <;f seven examined, were they ' able 

 to examine the parents as well as the children and the records 

 in this case (Family I) proved of great interest '. ' In all the other 

 families,' they continue, 'we examined the children only. . 

 It is of great importance to keep clearly in mind that these are 

 the results of one examination only. They are therefore minimum 

 results. At least the infections recorded were present ; probably, 

 in fact almost certainly, others also.' Their results are recorded 

 in a table {op. cit., Table V, p. 366), which need not be copied here 

 in full. On account of its great interest, however, and as an 

 example of the results obtained, I give below— in a modified 

 form — the findings for Family I. 



