634 PROCEEDINGS OF SECTION I. 



with five in the xinpurified water. With the latter the gelatine 

 was all liqnefied in three or four days, while with the former 

 liquefaction was not comijlete after as many weeks. (It is intended 

 to continue these experiments.) 



The comparatively small number of bacteria found in the mains 

 of the different water supplies that have been tested by me (see Table 

 8), viz., from sixty-four to 266, appears very small if w^e remember 

 that all are unfiltered surface waters ; and, taking the numbers 

 only into consideration, the waters w^ould probably all be passed as 

 healthy. The reason for this small number of bacteria is explained 

 by the experiment in Table 7, already quoted, where from the 

 sample taken as deep as possible not a single colony developed, 

 while a sample taken from the surface contained about 500,000, 

 and by the fact that the water is taken from the reservoii-s by a 

 valve about 16ft. from the surface. The number of species of 

 bacteria whiih could be distinguished from the different aspects of 

 the colonies when examined by a Coddington lens amounted in the 

 Adelaide and Mitcham waters to twelve, and nearly all of these 

 proved to be bacilli when examined under the microscope. This 

 large number of species with the comparatively small number of 

 bacteria renders these waters of a suspicious quality. It will be 

 seen, on comparing Table 8 wiih Table 6, that the number of 

 bacteria in the waters varies directly with the turbidity, and it 

 would appear that to a great extent the majority of the species are 

 attached to small particles of suspended matter. In order to 

 correctly gauge the significance of finding twelve species of 

 bacteria in Ic.c. of water, cultivated at 22° C. on nutrient gelatine 

 after three days' growth wnth access of sterile air, we must re- 

 member — 



1. That some species, mostly pathogenic, only develop at a 



temperatui-e of about 37° C. 



2. That others require wrecks before the colonies have develojDcd 



sufficiently to become visible to the naked eye. 



3. Others again do not develop at all in the nutrient gelatine. 



4. The purely anaerobic species develoj) only when air is 



excluded. 



5. Some requii-e the presence, others the absence, of light. 



6. Colonies which appear alike macroscopically may belong to 



altogether different species. 



7. The small quantity of water necessarily taken for each test. 



8. The liquefaction of the gelatine frequently putting an end to 



further observation after two or three days. 



So that where twelve species are found as above, there are- 

 probably many more kinds actually present, and the species which 

 have not developed are more likely to be pathogenic ones. 



I regret that the limited time and apparatus at my disposal have 

 prevented my going more fully into the bacteriological study of 

 our w^ater sujiplies, but think at the same time that the few experi- 

 ments I have been able to make fullv confirm the results of the 



