296 



WATKU-srrn.Y or towns in thf, rnorics 



Classes of 



faxal 



organisms 



111 accordimc-u with liis sflii'iiii; of woik Major ('Iciiii'slia ihcii iiiKltilook l>\ iiigfiiious 

 iiinl laborious methods to tleterininu tho efl'cct of sunlight on fiecal organisms. From 

 Laiwnitory experimunts it apiicarL'd : 



1. Tliat tile sun has a very powerful action in destroying all lajcal organisms in 

 water, particularly when they are " naked " and not surrounded by mucus derived from 

 the intestine ; 



2. That all fiocal organisms do not possess the power of resisting the action of 

 sunlight to an equal degree ; 



3. That it is possible to divide faecal organisms, with a reasonable degree of accuracy, 

 into the following classes : - 



(i) The delicate organisms or those that are very susceptible to the action of sunlight ; 



(ii) An intermediate class containing a very large number of organisms which occupy 

 an intermediate position between the two extremes; and 



(iii) The resistant organisms or those capable of resisting the action of sunlight for 

 a considerable length of time. 



While from weekly analyses of water from a neighbouring lake it was found: — 



1. That the action of the sun is powerful in destroying the fa>cal organisms and 

 that the surface layers of any large volume of water are in consequence purer than the 

 deeper ones. 



2. A practical point, following on this statement, is that the outlet from a reservoir 

 should be arranged as near the surface as is possible. 



3. That these analyses show that, in the Red Hills lake, bavilluK rlmic/e is by far 

 the commonest fajcal organism isolated from the bottom. 



4. That cdli ciimiaiDii!! even in large numbers, in a huge volume of water, disa))pear 

 with great rapidity. In the results obtained from the Eed Hills lake the organisms never 

 survived longer than six days. 



5. There is some evidence in these results, though as yet it cannot be taken as 

 thoroughly established, that, under certain conditions, the middle layers of a lake of over 

 12 feet deep contain more water organisms and more fajcal bacilli than the bottom or 

 the surface. 



6. That, when taking samples of lakes, ponds, etc., the depth from which the sample 

 is taken should be carefully stated. 



Further investigations on these lines apparently proved : — 



1. That the hacilliiii cloucue and (jriinthat will persist in water exposed to the action 

 of sun and storage for many months, and may therefore be looked upon as resistant to 

 these forces 



2. That the rareness of such organisms as coU communis in the samples analysed 

 demonstrates the fact that organisms very susceptible to the action of sunlight do exist ; 

 coli cinninunis being the commonest example of these. 



3. That there exists a large class of organisms, which in point of power of resistance 

 to the action of sunlight and storage, come between the very resistant and the susceptible 

 organisms. This class is made up of many species. Further investigation may make it 

 possible to sub-divide this large group. 



4. That storage, an important factor in which, in the Tropics, is the action of sunlight, 



to sunlight as jg capable of rendering a highly contaminated water extremely pure, and of killing a verv 

 a basis for r i r i • !■ 1 1 • 



■ i^'isificaiion g'"eat percentage of the fa;cal organisms present after gross pollution. 



.'\s a result of all this work it was evident that delicate organisms such as IS. mli 



communis and oxytocus peniiciosus exist in nature along with resistant forms, of which 



.Susceptibility 



