250 INTESTINAT, BACTERIA 
film is parallel with the long axis of the slide. By laying the slide over 
coordinate paper these diagonals are readily brought mto the same line 
parallel with the edge of the slide. 
‘The covers must be so mounted that these diagonals, now in a 
straight line, are those which crossed each other as tl.e two coverglasses 
were originally put together in preparing the films. When properly 
made each diagonal measures almost exactly 25 mm. 
“For counting the bacteria in the preparation, the Leitz 1/12 oil 
immersion objective and the No. 3 ocular fitted with an Ehrlich ocular 
square to restrict the field to a convenient size, and a mechanical stage 
oraduated in millimeters are employed. Beginning at the end of the 
diagonal of one coverglass the bacteria are counted in each of 25 fields 
1 mm. apart along this diagonal. In a similar way 25 fields are counted 
on the diagonal of the second coverglass, making a total of 50 fields, 
the average of which may be considered as representative of both films. 
The size of the sauare field is accurately measured by a stage microm- 
eter. From the data then at hand the number of bacteria per milligram 
feces is calculated. 
“ Example. B252, Subject H, July 15, 1908. In the preparation 
made, as described, each film measures 16.5X17.5 mm., total film area 
therefore, 3317.5 mm.; the field employed measured 0.0445 mm. 
square; the amount carried by the loop 2.01 mg.; the number of bac- 
teria counted in 50 fields was 559 and the original 1: 100 suspension 
was used (diluted to 1: 200 by dye and gelatin). From these data, 
, qq: 559X383 X 17.5 X 200 
Bacteria per milligram feces = 575 aad 9c0.O14B C201 O00. 
In this fraction all the members except the size of the films and the 
number of bacteria counted may be kept constant and the calculation 
simplified by the use of logarithmic tables. 
‘With apparatus and reagents ready and the 1: 100 suspension 
prepared, this entire estimation can be completed in about forty min- 
utes. The results cannot be considered very accurate as the platinum 
loop does not carry an exactly constant quantity. There is also some- 
times great difficulty in distinguishing micrococci from other fine par- 
ticles in the preparations. The concentration of the bacterial suspen- 
sion also influences the final result. The estimation is in general rela- 
tively higher when dilute suspensions are counted as we have observed 
in applying it to enumeration of bacteria in pure cultures.” * 
Steele’s Modification of the Strassburger Procedure for the Quanti- 
tative Enumeration of Fecal Bacteria. Steele describes the method as 
* From MacNeal, Latzer and Kerr. J. Inf. Dis. 6 (1909), p. 127. 
