MEDICAL MILK COMMISSIONS AND CERTIFIED MILK. 31 
clave sterilization ; in such, cases distilled water may be used or the auto- 
clave pressure increased. With dilution water in 8-ounce bottles calibrated for 
99 cubic centimeters * * * all the necessary dilutions may be made. 
Short, wide-mouthed "blakes" or wide-mouthed French square bottles are 
more easily handled and more economical of space than other forms of bottles 
or flasks. 
Eight-ounce bottles are the best, as the required amount of dilution water 
only about half fills them, leaving room for shaking. Long-fiber nonabsorbent 
cotton should be used for plugs. It is well to use care in selecting cotton for 
this purpose to avoid short-fiber or dusty cotton, which give a cloud of lint-like 
particles on shaking. Bottles * * * should be filled a little over the 99 
c. c. * * * to allow for loss during sterilization. 
Pipettes. — Straight sides 1 c. c. pipettes are more easily handled than those 
with bulbs ; they may be made from ordinary three-sixteenths inch glass tubing 
and should be about 10 inches in length. 
Plating technique. — The agar after melting should be kept in the water- 
jacketed water bath between 40° C. and 45° C. for at least 15 minutes before 
using to make sure that the agar itself has reached the temperature of the 
surrounding water. If used too warm the heat may destroy some of the bacteria 
or retard their growth. 
Shake the milk sample 25 times, then with a sterile pipette transfer 1 c. c. to 
the first dilution water and rinse the pipette by drawing dilution water to the 
mark and expelling ; this gives a dilution 1 to 100. 
* * * Then with a sterile pipette transfer 1 c. c. to the Petri dish, using 
care to raise the cover only as far as necessary to insert the end of the pipette. 
Take the tube of agar from the water bath, wipe the water from outside the 
tube with a piece of cloth, remove the plug, pass the mouth of the tube through 
a flame, and pour the agar into the plate, using the same care as before to 
avoid exposure of the plate contents to the air. 
Carefully and thoroughly mix the agar and diluted milk in the Petri dish by 
a rotary motion, avoiding the formation of air bubbles or slopping the agar, 
and after allowing the agar to harden for at least 15 minutes at room tempera- 
ture, place the dish bottom down in the incubator. 
Plating should always be done in a place free from dust or currents of air. 
In order that colonies may have sufficient food for proper development 10 c. c. 
of agar shall be used for each plate. 
67. Determination of taste and odor of milk. — After the plates have been pre- 
pared and placed in the incubator, the taste and odor of the milk shall be deter- 
mined after warming the milk to 100° F. 1 
68. Counts. — The total number of colonies on each plate should be counted, 
and the results expressed in multiples of the dilution factor. Colonies too 
small to be seen with the naked eye or with slight magnification shall not be 
considered in the count. 
69. Records of oacteriologic tests. — The results of all bacterial tests shall be 
kept on file by the secretary of each commission, copies of which should be 
made available annually for the use of the American Association of Medical 
Milk Commissions. 
CHEMICAL STANDARDS AND METHODS. 
The methods that must be followed in carrying out the chemical investiga- 
tions essential to the protection of certified milk are so complicated that in 
order to keep the fees of the chemist at a reasonable figure, there must be 
eliminated from the examination those procedures which, whilst they might be 
helpful and interesting, are in no sense necessary. 
For this reason the determination of the water, the total solids and the 
milk sugar is not required as a part of the routine examination. 
70. The chemical analyses shall be made by a competent chemist designated 
by the medical milk commission. 
1 Should it be deemed desirable and necessary to conduct tests for sediment, the pres- 
ence of special bacteria, or the number of leucocytes, the methods adopted by the com- 
mittee of the American Public Health Association should be followed. 
