346 



PUBLIC HEALTH BACTERIOLOGY 



Allow the sterilizer to cool, then stopper the bottle, and 

 remove and put in case. 



In sampling from a tap, run the water to waste for half 

 an hour, and then fill bottle. Stopper, and label with 

 particulars of place, time, and date. Examine at once, 

 or pack in ice to prevent multiplication of organisms. 



In sampling from a lake, dip stoppered bottle well below 

 surface ; remove stopper, and keep it under water ; allow 

 bottle to fill ; replace stopper, and bring bottle to surface. 

 Pack in ice. 



Examine samples as soon as possible after collection. 

 Keep in ice in meantime. 



Dilutions. If the water is pure, no dilution will be 

 required ; if impure, varying dilutions are used according 

 to the degree of impurity. These may be made by the 

 decimal mode of dilution described on page 367 ; or flasks 

 may be kept ready containing 100 c.c. of sterile water. 

 One c.c. of sample added to such a flask by sterile pipette 

 gives practically a dilution of 1 in 100 ; 1 c.c. from this 

 flask to another sterile 100 c.c. gives 1 in 10,000 ; and so on. 

 To get 1 in 10, remove 10 c.c. by sterile pipette, and add 

 10 c.c. of sample ; and from this dilution others are simi- 

 larly made. 



Standards. 



Deep wells and springs \ 



Surface waters : 

 Shallow wells 

 Cultivated lands 

 Rivers 



Bacterial Count. 



Gelatin Plate 

 at 20 C. 



Should not 



exceed 

 50 per c.c. 



Ditto 

 500 per c.c. 



Agar Plate 

 at 37 C. 



Should not 



exceed 

 10 per c.c. 



Ditto 

 50 per c.c. 



Bacillus 



Coli 



Communis. 



Should be 



absent 

 in 100 c.c. 



Ditto 

 in 10 c.c. 



Methods of Water Examination. These are based 

 on the knowledge that the dangerous organisms in water 

 are usually present from sewage pollution. Inasmuch as 

 some of these forms are not easily isolated from water, the 

 mode of procedure is to ^enumerate the total bacterial 

 content, and to look for an organism, likewise present from 



