16 The Philippine Journal of Science ms 



(1.5 to 2.0 per cent agar, 1 per cent lactose). The reaction of 

 this medium is almost neutral, there being present barely enough 

 alkalinity to give a slight blue. It is put up in test tubes, in 

 10 cubic centimeter portions, and is thoroughly sterilized. 



The Petri dishes used for the plate cultures are packed in 

 individual envelopes and then sterilized. The envelopes, made 

 of heavy Manila paper, are about the same width as the dishes 

 and about twice as long as they are wide. Packages of six 

 plates, well wrapped with paper, may be transported with little 

 danger of breakage and will remain sterile indefinitely. 



The pipettes used hold 1 cubic centimeter and are about 20 

 centimeters long. If these are not available, they may be readily 

 made from glass tubing. The pipettes in lots of six are well 

 wrapped in cheesecloth, having several folds of cloth between 

 one pipette and the next. The ends of the package are tied 

 "together, and the package is inserted in a tin can just large 

 enough for the purpose. The closed tin can containing the 

 pipettes is then sterilized. While warm, the can is sealed with 

 adhesive tape. When cool, the tape is well covered with paraffin. 

 Pipettes so packed will remain sterile almost indefinitely. 



For several kinds of work sterile bottles may be employed. 

 Instead of the ordinary cotton plugs, which are often either 

 pushed in or which come out during transportation, we use a 

 cotton-covered cork. This arrangement has been found very 

 satisfactory. 



Ordinarily two plate cultures and one tube culture are made 

 of each sample. Three tubes of media are thus required. The 

 tubes are melted by heating in water over an alcohol lamp and 

 are then cooled to 45°. 



Plating is done at a temperature of from 40° to 43° C. For 

 a water such as that from a spring or artesian well, believed to 

 be comparatively pure, 0.5 and 1.0 cubic centimeter cultures 

 are made. For a water suspected of contamination, plates may 

 be made of 0.2, 0.1, or 0.05 cubic centimeter, depending on the 

 apparent degree of contamination. The water is introduced 

 into the Petri dish, the liquified agar is added, and the plate is 

 manipulated to insure thorough mixing. After complete cool- 

 ing, the plates are returned to their envelopes and carried in 

 an inverted position to prevent spreading of the colonies by 

 water of condensation. 



The tube culture for the presumptive test is made by intro- 

 ducing the desired amount of water into the tube of liquified 

 agar and mixing thoroughly by agitation. Usually 1 cubic centi- 

 meter is taken for this test, though more or less may be em- 



