252 INTESTINAL BACTI RIA 
portion of alcohol, and evaporated down slowly at a temperature of 
40° to 50° C. until it amounts to not more than 50 ¢.c. in all. This 
takes approximately twenty-four hours. It is then mixed with at least 
twice its volume of alcohol, preferably absolute alcohol, although this is 
not absolutely necessary. This lowers the specific gravity of the fluid 
to such an extent that now the bacteria readily centrifugalize out. 
The mixture is then centrifugalized until the supernatant liquid is 
quite clear. This takes thirty minutes or more for each tube. The 
residue, which consists of the bacteria, is washed with pure alcohol and 
is shaken up with ether to remove the fat; then it is again washed with 
alcohol. All of this washing is done by means of the centrifuge. The 
bacteria are next washed out of the tube with a little alcohol and evap- 
orated to dryness and dried in the oven at moderate heat, dried in the 
desiccator, and weighed. Smears of the final preparation show that 
it consists of bacteria with a very few minute particles of other material. 
These particles are only visible with high power, and are very few in 
number, perhaps two at each field of the 1/12-inch objective. They 
stain with methylene blue; Strasburger suggests that they are cellulose, 
which they may well be. At any rate, the error arising from the inclu- 
sion of these small particles in the dried weight of the bacteria must be 
very small, and is probably balanced by the bacteria that it 1s not pos- 
sible to wash out of the residue in the first washing. During the prep- 
aration of the bacteria the first portion of 5 c.c. has been dried and 
weighed. We then know the dried weight of 5 c.c., the weight of the 
dried bacteria in 5 ¢.c., the original volume of the stool, and the volume 
after the addition of a known amount of water. It is then easy to cal- 
culate the data that we desire, namely, the volume of the stool, its dried 
weight, the weight of the dried bacteria, and the percentage of bacteria 
in the dried weight.”’ 
Mattil and Hawk’s Method for Quantitative Determination of Fecal 
Bacteria. “‘ The method is a simplification of MacNeal’s adaptation of 
the Strasburger procedure. About 2 gms. of feces are accurately 
weighed and placed in a 50-c.c. centrifuge tube. To the feces in the 
tube a few drops of 0.2 per cent hydrochloric acid are added, and the 
material is mixed to a smooth paste by means of a glass rod. Further 
amounts of the acid are added with continued crushing and stirring 
until the material is thoroughly suspended. The tube is then whirled 
in the centrifuge at high speed for one-half to one minute. The sus- 
pension is found sedimented in not more or less definite layers, the upper- 
most of which is fairly free from larger particles. The upper and more 
liquid portion of the suspension is now drawn off by means of a pipette 
