Quantitative aspects of sampling leprosy skin lesions by the scraped incision method

ABSTRACT

1- The problem of obtaining more useful and convenient estimates of the numbers of M. leprae in material from scraped skin incisions has been investigated by demonstrating (a) that the spreading of small samples on glas slides causes very rapid dilution; (b) that the areas filmed should be proportional to the volume of samples; (c) that variability in present practical results may often be due to attempts to spread the variable samples on standard areas; and (d) that this practice results in over-dilution and in irregular distribution of components within the films. 2- A study of the art of preparing uniform films on slide areas which are proportional to unknown volumes of sample leads to the suggestion that each sample be spread to the maximal limit which permits a natural redistribution of the cellular components before drying begins. Enumerations reveal that this modification of habit results in a predictable distribution of bacilli. 3- Increased sensitivity, when desired, may be achieved by increasing the thickness of film to 4 times that recommended for routine purposes. Such films may be on the order of 14 times more sensitive than average films, and 56 times more sensitive than the thinnest clinical films which were available for analysis in this study. A second means of increasing sensitivity is to examine all tissue fragments and cell clusters in each film.