186 APPENDIX. 



Boiling as a means of purifying. When such a filter cannot 

 be obtained, the only alternative is to boil all the water to be 

 used for drinking ; and this should especially be done in times 

 of typhoid and cholera epidemics. 



Methods of Examination. Since the germs rapidly multiply 

 in stagnant water, an examination must not be delayed longer 

 than an hour after the water has been collected. Every pre- 

 caution must be taken in the way of cleanliness to prevent con- 

 tamination ; sterilized flasks, pipettes, and plugs must be at 

 hand, and the gelatine tubes best inoculated on the spot. If 

 this cannot be done, the sample should be packed in ice until 

 it arrives at the laboratory. The sample is placed in a steri- 

 lized glass flask, and the flask then closed with a sterile cotton 

 plug. A sterilized pipette is then dipped into the flask and 

 1 c.c. of the water withdrawn and added to a tube of gelatine, 

 the gelatine being in a fluid condition. To a second tube, 

 \ c.c. is added. The tubes are then shaken so as to thor- 

 oughly mix the water with the gelatine, and then poured 

 upon wide glass plates, one plate for each tube ; the plates are 

 then placed in the moist chamber, and in two or three days 

 examined. A temperature of 18 to 20 C. is best. Many water- 

 bacteria are hindered by higher degrees of heat. If the germs 

 are equally divided, there should be one-half the number on 

 one plate that there is on the other; thus the \ c.c. serves as 

 control. 



Water that is very rich in germs requires dilution with ster- 

 ilized water 50 to 100 times. Fewer colonies will be found on 

 agar than on gelatine even at the same temperature. 



To count the colonies which develop upon the plates, a spe- 

 cial apparatus has been designed, known as 



Wolfhiigel's Apparatus. A glass plate divided into squares, 

 each a centimeter large, and some of these subdivided. This 

 plate is placed above the gelatine plate with the colonies, and 

 the number in several quadrants taken, a lens being used to 

 see the smaller ones. 



The petri saucers can be used instead of plates, and an appa- 

 ratus on the Wolf hugel plan can be obtained to count the colo- 

 nies. It is best to count all the colonies on the plate or dish. 



