﻿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 S-ounce bottles calibrated for 

 99 cubic centimeters * * * all tbe 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. 



