The true efficiency of a single iodine- or hematoxylin-stained fecal film for the detection of Endamoeba histolytica infections was less than one in five, and ten examinations had to be made to make a negative result reasonably reliable. By a combination of one of these technics with zinc sulphate centrifugal floatation about one out of three or four infections was detected in a single examination, while five examinations provided a probability of 70 to 90 per cent.
The efficiency of the iodine- or hematoxylin-stained film for the non-pathogenic protozoa was one in four, and five examinations detected about 80 per cent. However, when one of these two technics was combined with zinc sulphate centrifugal floatation, the probability was about one in two, while three examinations detected more than 80 per cent.
Thus, the use of the zinc sulphate centrifugal floatation technic in combination with the direct fecal film examination provides greater reliability and ease of detecting intestinal protozoa with fewer specimens than does either of the non-concentration technics.