Frost—Bacteriological Control of Public Milk Supplies . 1315 
Other pipettes were carefully cleaned with soap and water 
and then immersed in alcohol for a few minutes, dried, and after 
sterilization in the dry-air sterilizer for 1 hour at 150° C. were 
found to be free from grease and entirely satisfactory. 
It seems, then, quite sufficient in cleaning pipettes to get them 
bright and clear by the use of water or soap or soap-powder, and 
then immerse them in alcohol for several minutes. "When dry 
they are then ready to be sterilized. 
III. A Mechanical Volumetric Pipette, or Pipettometer. The 
pipettes used for the purpose of diluting milk are of various 
types. Those carefully graduated to tenths or hundredths of a 
c.c., and frequently used, are expensive. With ordinary 
pipettes there is the danger that in using them the saliva may run 
down into the material being measured. This can be prevented 
by inserting a small plug of cotton in the end that is put in 
the mouth. It requires a good deal of time to put in the 
plug and later to take it out. Another danger, where the ma¬ 
terial worked with contains pathogenic germs, is that these may 
be accidentally sucked into the mouth—a catastrophe that has 
too often brought dire results to laboratory workers. The follow¬ 
ing simple devise obviates many of the objections raised as ap¬ 
plying to the use of pipettes in general, and will be found use¬ 
ful for routine as well as special work, if not on all occasions. 
It was suggested by the pipette holder described by Rosenau* 
and may be considered a modification of it. It can best be de¬ 
scribed by reference to the accompanying figure. Pig. 5. 
A is a wooden support with a short arm on the left, and a 
broad arc on the right. The whole is supported by a heavy 
base A. On this is a bent glass tube (a, b, c, d) with a flexible 
joint at c, and a bulb at d. This tube is filled with mercury 
from e to d. When the arm (B) is moved to I, the mercury 
stands at 1.0, and when the arm (B) is lowered to II, the mer¬ 
cury stands at 0. The end of the glass tube (at a) is fitted with 
a rubber tube into which a' pipette may be readily slipped (g). 
The apparatus is used, by raising the arm (B) to I, a vessel con¬ 
taining the fluid to be drawn up into the pipette is brought up 
to the point of it and then the agm (B) is lowered to II. In this 
way the fluid is drawn into the pipette. It can then be dis¬ 
charged in whole or in part by raising the arm (B). The gradu- 
* Hyg. Lab. Bull. 21, Gov’t. Print. Office, 1905, p. 62. 
