PART I. INCIDENCE 13 



single examination would have to be multiplied by three in 

 order to arrive at a correct result. Whether this is too high an 

 estimate future investigations will show, but it seems to us that the 

 findings of a single examination are far below what they really 

 should be and that to triple the figures would give a result much 

 more nearly accurate. The findings amongst the various groups to be 

 described now are all based on the single examination, with the pos- 

 sible exception of a very small number of hospital cases which have 

 been examined two, three, or even more times. It will be realized 

 that the figures, though they may appear high, are very much lower 

 than they would have been if the examinations had been repeated. 



One important point requires mentioning, and that is the 

 possibility of the errors of a single examination being less when 

 the organism is the actual cause of disease. For instance, when 

 lamblia is the cause of diarrhosa with mucus, it is present in 

 enormous numbers and there is no chance of missing it on first 

 examinations. It is only when it is not producing symptoms that 

 it is likely to be overlooked. Similarly, if E. histolytica is giving 

 trouble, the probability is that the amoebae or its cysts will be found 

 at once. These errors, therefore, in the single examinations do not 

 appear, or appear to a much smaller extent in those cases where 

 the organism looked for is the actual cause of trouble. The error 

 is the greatest in the search for carriers, and it is a consolation to 

 know that if any infection is missed it is unlikely to have been the 

 cause of trouble to the individual himself at the particular time, 

 though it must never be forgotten that the E. histolytica carrier is 

 the constant source of infection for others. 



It should be mentioned that the records in Table I are based 

 on thorough and careful examinations. For example, the time 

 spent on the daily examination of any one case was not less than 

 ten minutes, and in most instances at least two or three films were 

 subjected to a close scrutiny. 



Examination of Various Groups of Men for Protozoal Infections. 



(a) Healthy Troops. An examination of a large number (1,979) 

 of healthy men on full duty was undertaken with the object of dis- 

 covering the percentage of carriers of various protozoa, especially of 

 E. histolytica. The samples for examination were collected in the 

 manner described above. The following groups were examined : 



Metras camp, 1,013 men. 



Mustapha Convalescent Depot, permanent staff, 312 men. 



