1312 Wisconsin Academy of Sciences, Arts, and Letters. 
stoppers and a paper cap. It should be noted, however, that 
there was practically no checking of evaporation by the use of 
thin paper caps in the experiment described above. The use of 
waxed paper or tin foil will be found efficient. Except for the 
trouble in opening, a very satisfactory procedure is to dip 
the cotton plug in melted paraffin. My own suggestion is that 
the mouths of the bottles be plugged with a cork stopper covered 
with a thin layer of cotton such as is used by the Boston Board 
of Health laboratory in their blood serum tubes. This reduces 
the opportunity foe evaporation to a minimum, while allowing 
for the necessary interchange of gases during sterilization. 
The neck of the bottle is then covered with paraffin paper, 
tied on with a string, this, of course, to be done before steriliza¬ 
tion. When the bottle is to be used this paper cap is to be care¬ 
fully removed and kept and then when the dilution has been 
made the cap is to be placed over the neck and the plug used to 
press, the paper into the mouth of the bottle. This closes the 
bottle as effectively as a glass stopper and allows thorough shak¬ 
ing of the sample—a matter of prime importance in quantita¬ 
tive work. Fig. 2, Plate XCIY. 
b) Dilution Scheme. Milks need to be diluted before they 
are plated. For certified or pasteurized milks a dilution of 
1-100 is usually sufficient. Milks of the inspected class fre¬ 
quently need to be diluted 1-1,000, while raw market milks need 
to be diluted from 1-1,000 to 1-100,000. The scheme indicated 
in the following diagram (Fig. 3.) gives at a glance the proce¬ 
dure necessary to obtain the desired dilution. A microscopical 
examination of a milk by the Stewart-Slack method is sometimes 
of value in determining the dilution needed for a particular 
