10 
Method of examination. — The method used for diagnosis through- 
out the investigation has been that of microscopic examination of the 
feces for the eggs, larvae, or adult forms of the parasites. The exami- 
nations were made as thorough as possible by studying not less than 
10 cover-glass preparations of each fecal specimen and by having at 
least two men work independently on each set of preparations. 
Careful measures were taken to prevent mutual or outside contami- 
nation of the specimens during their collection and examination. 
As is generally recognized, microscopic examination of the feces is 
an uncertain method of diagnosing the presence of the pinworm. 
Therefore only minimum statistics can be claimed for our figures for 
this parasite, the possibility being present that the number of infec- 
tions was greater than actually found. It is possible, also, that the 
eggs of certain tapeworms, especially of Tsenia, are not constantly 
present in the stools in the case of an infection with these parasites. 
The ova of some nematode worms have been said to disappear tempo- 
rarily from the feces during an infection, but probably such disap- 
pearance would be exceptional and due to special conditions, as when 
the patient is under anthelmintic or purgative treatment or perhaps 
when he indulges unduly in some food or drink or takes some drug 
which has a stupefying effect on the parasites. 
The possible temporary absence of ova in the feces of persons 
infected with intestinal worms should, of course, be taken into account 
in considering the results of our own work as well as the results of all 
other investigations of a similar nature conducted by examination of 
the feces. Such a possibility could be guarded against only by 
repeated examinations of each patient, which, if the work were on a 
large scale, would necessarily mean to narrow the basis of the investi- 
gation, that is, to examine fewer patients. In our own experience, 
while the number of eggs in the feces of an infected patient varied 
considerably at different times, it was rare that no eggs could be found 
in examining 10 cover-glass preparations of the feces of a patient 
who had previous^ been found infected; there seems little doubt, 
therefore, that a more practical index of the amount of infection with 
intestinal worms in a community will be obtained by making a single 
examination of as many- people as possible by the above method (10 
preparations) than by making two examinations at different times 
of one-half as many people or three examinations of one-third as many 
people. 
The technique of the microscopic examinations was simpfy to add 
to a very small amount of feces a drop or two of water on a 2 by 3- inch 
glass slide, cover it with a three-fourths inch square cover glass, and 
examine with a moderate power lens, either an 8 mm. or a one-third 
inch objective being sufficiently strong for a person familiar with 
the appearances of the various ova. Very fluid stools need no dilu- 
tion. We found that diluting the feces, and thus obtaining a uniform, 
