1314 Wisconsin Academy of Sciences, Arts, and Letters. 
then the “tube” pipette. The plates were grown at room tem¬ 
perature and counted six days later. There were only a few 
colonies on the plate and all were, therefore, counted. 
Ordinary pipettes, plate 1 . 78 colonies 
plate 2 . 76 colonies 
plate 3 . 65 colonies 
plate 4 . 77 colonies 
Tube pipettes, plate 1 . 63 colonies 
plate 2 . 31 colonies 
plate 3 . 84 colonies 
plate 4 . 73 colonies 
The percentage of variation in the first set was 17%, in the 
second case it was 84%, or practically five times as great. 
The shape of the pointed end and the size of the opening are 
matters of some importance. The smaller the opening the more 
accurate the pipette. If the point is drawn out fine, the less 
fluid is likely to be taken up by it on the outside of the pipette 
to run down and increase the volume of the discharge. On the 
other hand, such points are easily broken and furthermore, if 
cleaning solutions are used, there is the greater probability that 
the chemical may not be perfectly washed out. Again, such 
pipettes are slower and require considerably more time. It 
seems reasonable that such pipettes should have an opening of 
about 2 mm. and should be drawn out to a point and not merely 
rounded off in the flame. 
II. Method of Cleaning Pipettes, The matter of cleaning 
pipettes is of considerable importance, not merely because they 
ought to be kept bright and clear, but because, especially when 
they are used for milk, they become greasy and do not deliver 
all of their contents since a part of it sticks to the sides. 
It is the custom in many laboratories to clean these pipettes 
by immersing them for several days in a cleaning solution made 
from sulphuric acid and potassium bichromate, then washing 
them in water, or first in alcohol and then water. This requires 
several days. Some experiments were made for the purpose 
of determining whether or not it would be as satisfactory to 
clean the pipettes well in soap and water and then sterilize them 
at a high degree of heat, say 250° 0., for a time in order to dry 
distill the organic matter. This method does not seem to suc¬ 
ceed, at least at a reasonable temperature within a reasonable 
length of time. 
