BACTERIA IN FECES 251 
follows: ‘‘ The possibility of separating the bacteria from the rest of 
the feces depends on the fact that the bacteria are so nearly of the same 
specific gravity as distilled water that they cannot be centrifugalized 
out of a watery suspension of the feces, but remain suspended in the 
supernatant fluid. Taking advantage of this, the bacteria can be 
removed by washing with the centrifuge. Then, if the specific gravity 
of the wash-water is lowered by the addition of large amounts of alcohol, 
the relation of the bacteria to the fluid is changed to such an extent that 
the microorganisms can be readily centrifugalized out, separated, and 
weighed. Unless the period of passage of the feces has been ascer- 
tained to be normal, it is better to mark the beginning and end of each 
period of examination by carmine. The use of the Schmidt diet is not 
necessary. The whole stool is saved. Unless the feces are liquid they 
are rubbed up with a known amount of distilled water until they are 
smooth and semi-liquid and as homogeneous as it is possible to make 
them. 
‘Two portions of 5 cc. are measured off with a pipette of large 
caliber, using for this purpose an ordinary 5 c.c. pipette with the tapering 
end cut off, and with the necessary correction made at the upper mark. 
One of these portions of 5 ¢.c. is put into a porcelain dish and dried over 
a water bath and later in a drying oven, in order to determine the dricd 
weight. The addition of a little alcohol and thorough mixing will hasten 
the process of drying and prevent caking of the feces. 
‘“‘ The second portion is washed free from bacteria. This is done as 
follows: The wash-watér is 0.5 of 1 per cent HCl solution in distilled 
water. The acid increases the solubility of the salts and soaps of the 
feces. One hundred c.c. of this solution is employed at the beginning 
of the washing The feces are thoroughly mixed with the wash solu- 
tion and then centrifugalized. The use of the water motor or electric 
centrifuge is almost essential. Each tube is centrifugalized for about 
14 minutes, then the cloudy supernatant liquid is poured through a 
layer of gauze. This fluid contains the bacteria in suspension. All of 
the mixture (the wash-water and the feces) is centrifugalized the same 
way, and then the residue in the tubes is shaken up with more of the 
wash-water and centrifugalized again. This is repeated until the super- 
natant liquid after the centrifugalizing is transparent, showing that 
approximately all the bacteria have been washed out. If smear is made 
of the residue at this point, it will be found that the bacteria are not 
entirely washed away, but are evidently very much reduced. They 
occur singly, while in the unwashed feces they are in great lumps and 
masses. The suspension of bacteria is then mixed with a liberal 
