SOUTH AUSTRALIAN WATER SUPPLY. 633 



into our reservoirs, and especially' of flood water, introduces much 

 life and food for life with it. Bacteria, algse, and infusoria abound, 

 and the latter afford food for fishes, which in some reservoirs, into 

 which turbid water has been introduced, multiply very fast. 

 Many of them doubtless die in the reservoir and supply food for a 

 fresh crop of bacteria, &.C., while others, issuing from the service 

 taps and blocking the meters, awake the public to the fact that our 

 waters are not all that they should be. It is indeed notable that 

 most of the complaints as to the impure state of our waters are 

 made at a time when they are, as regards organic purity, at their 

 best. 



In Table 7 the resvdts of a series of experiments on bacteria in 

 the Adelaide service water are given. A number of Wynchester 

 quarts of this water -were drawn at the same time from the service 

 pipe, the bottles having been thoroughly cleansed ; of these one-third 

 were untreated, one-third were purified by the Anderson process 

 and the water decanted, the remainder treated by a modification 

 of the Anderson process. To test the number of bacteria in the 

 wnters Ic.c, or less, of water was mixed with sterile nutrient 

 gelatine and povu'ed into a sterilised bottle, on the sides of which 

 it was spread evenly, and allowed to solidify. The bottle was then 

 placed in an incubator at about 22° C, and the number of colonies 

 counted after two or three days. Blank experiments were made 

 to prove that no growth occurred when sterile water was used. 

 The number of bacteria is always given per cubic centimetre. 

 The number of bacteria in the water was reduced from 320 per 

 cubic centimetre in the original, when first drawn, to only 5 in 

 the purified water, after standing two days, while in the untreated 

 water the number had increased to 180,000 in the same time, this 

 being the maximum number obtained in the untreated water, 

 probably in consequence of the presence of infusoria in the water, 

 which kept the bacteria from excessive development. The 

 advisability of using freshly-drawn water for drinking purposes in 

 preference to that which has been standing for some time is very 

 evident from the above. 



The number of bacteria in the purified waters rapidly increased 

 until after standing seven days; they each contained about 

 700,000. Two days later a sample was very carefully taken at 

 9in. from the siirface of the same bottle, and this, after cultiva- 

 tion and keeping for several weeks, did not develop a single 

 colony. It would therefore appear that most, if not all, the 

 bacteria that flourish in what would be classed as an originally 

 pure water are aerobic and confined to the surface of the water. 

 After the seventh day the number of bacteria at the surface in the 

 purified water gradually decreased, and according to the last 

 experiments is still decreasing, probably owing to most of the food 

 material having been exhausted, as all infusoria must have been 

 destroyed during the purification of the water. The number of 

 species found in the water after two months was three, as compared 



