APPENDIX. 367 



teristics. The importance of a thorough acquaintance 

 with the life-history of the individual micro-organisms 

 cannot be too strongly insisted upon. For example, by 

 such means the spirillum of Asiatic cholera can be dis- 

 tinguished from other comma-shaped organisms, and 

 inasmuch as its presence may be an indication of con- 

 tamination with choleraic discharges, such water should 

 be condemned for drinking purposes, even though we may 

 not yet be in a position to affirm that the microbe is the 

 cause of the disease. The test, in short, consists in making 

 plate-cultivations of a known volume of water, counting 

 the colonies which develop, isolating the micro-organisms, 

 and studying the characters of each individual form. 



Collection and Transport of Water Samples. 

 Erlenmeyer's conical flasks of about 100 ccm. capacity 

 may be employed with advantage for collecting the 

 samples of water. They are cleansed, plugged, and 

 sterilised in the hot-air steriliser. When required for use, 

 the plug is removed and held between the ringers, which 

 must not touch the part which enters the neck of the 

 flask. About 30 ccm. of the water to be examined are 

 introduced into the flask, and the plug must be quickly 

 replaced and covered with a caoutchouc cap. If collected 

 from a tap, the water should first be allowed to run for a 

 few minutes, and the sample should be received into the 

 flask without the neck coming into contact with the 

 tap. From a reservoir or stream the flasks may be filled 

 by employing a sterilised pipette. During transport con- 

 tact between the water and cotton-wool plug must be 

 avoided, and if likely to occur the sample must be collected 

 and forwarded in a Sternberg's bulb (p. 31). 



Examination by Plate Cultivation. The 

 apparatus for plate-cultivation should be arranged as 

 already described. Crushed ice may be added to the 

 water in the glass dish to expedite the setting of the 

 gelatine, so that the plate may be transferred as quickly 

 as possible to the damp- chamber. The caoutchouc cap 



