BACTERIA IN THE AIR. 621 
Glass tubing having a diameter of about five millimetres is used in 
making these tubes, and from one to two grammes of powdered sugar 
ix a suitable quantity to use asa filter. The whole apparatus is steril- 
ized for an hour at 150° C. in a hot-air oven after the pulverized 
sugar has been introduced. Before using it will be necessary to 
pack the sugar against the supporting plug a by gently striking the 
lower end of the tube, held in a vertical position, upon some horizon- 
tal surface; and during aspiration 
the tube must remain in a vertical 
position, or nearly so, in order that 
the sugar may properly fill its entire 
calibre. The aspirator is attached to 
the lower end of the tube by a piece 
of rubber tubing. When the tube B 
is used the sealed extremity is broken 
off at the moment that the aspirator 
is set in action, and it is again sealed 
in a flame after the desired amount 
of air has been passed through the 
filter. The next step consists in dis- 
solving the sugar in distilled water 
or in liquefied gelatin. To insure 
the removal of all the sugar the cot- 
ton plug a may be pushed out with a 
sterilized giass rod, after removing:b 
with forceps. From fifty to five hun- 
dred cubic centimetres of distilled 
water, contained in an Erlenmeyer 
flask and carefully sterilized, may be 
used, the amount required depending 
upon circumstances relating to the Y ss 
conditions of the experiment. By a 
adding five or ten cubic centimetres Sib 
of this water, containing the sugar es me site 36h 
and microérganisms arrested by it, 
to nutrient gelatin or agar liquefied by heat, and then making Es- 
march roll tubes, the number of germs in the entire quantity is easily 
estimated by counting the colonies which develop in the roll tubes. 
Sedgwick and Tucker, in a communication made to the Boston 
Society of Arts, January 12th, 1888, were the first to propose the use 
of a soluble filter of granulated sugar for collecting atmospheric 
germs. Their complete apparatus consists of an exhausted receiver, 
from which a given quantity of air is withdrawn by means of an air 
pump. A vacuum gauge is attached to the receiver, which is coupled 
